Knowledge as Objectively Justified Belief

Abstract

According to Lehrer’s defeasibility account of knowledge, we can understand knowledge as undefeated justified true belief. But this account faces many serious problems. One important problem is that from one’s subjective point of view, one can hardly bridge the gap between one’s personal justification and objective truth. Another important problem is that this account can hardly accommodate the externalist intuition that the epistemic status of a belief is not entirely determined by factors that are internal to the subject’s perspective. The goal of this paper is to offer an alternative account of knowledge which can successfully deal with these problems. On the basis of a Sellarsian social practice theory of justification, I argue that we can understand knowledge as objectively justified belief.

1 Preliminary Remarks

On the traditional tripartite definition of knowledge, knowledge is justified true belief. And most accounts of knowledge accept that knowledge implies truth. If so, we can determine whether a person, say S, knows that p only if we can determine whether “p” is true. The question then is how to determine whether “p” is true.

The first thing to note in this connection is that we cannot step outside our minds to judge that our own conceptual states agree with something external to them. As Otto Neurath (1959, p. 201) aptly puts it, “We are like sailors who must rebuild their ship on the open sea, never able to dismantle it in dry-dock and to reconstruct it there out of the best materials.” On this coherentist insight, we have no other way but to judge whether a belief is true on the basis of evidence or reason.

The second, related thing to note is that, as Ludwig Wittgenstein (1969, §§341–343) points out, a genuine doubt is possible only against a background of beliefs which are not doubted at the same time.

The third thing to note is that our concept of epistemic justification is a normative concept. In our epistemic discourse, we evaluate beliefs as justified or not on the basis of epistemic norms such as the one that one ought to believe propositions on the basis of adequate grounds. And we ought to accept justified beliefs, whereas we ought not to accept unjustified beliefs.

If the above considerations are on the right lines, we cannot rationally meet any demand for justification independently of our conceptual framework. What I mean by “a conceptual framework” here is a framework on the basis of which we can settle a genuine doubt or meet a demand for justification. Besides, as Kant (1996) insists, it is our conceptual framework that provides the norms, criteria, or rules for defending (or criticizing) any belief. If so, any demand for justification is not intelligible from outside of our conceptual framework.

One more important thing to note is that the deflationary conception of truth is very influential among truth theorists in the philosophy of logic.¹ On this conception of truth, truth is not a substantial concept. To illustrate, consider the following two statements:

• (1) Caesar was murdered.

• (2) It is true that Caesar was murdered.

If one person asserts (1) and if another person asserts (2), what they assert is exactly the same. This implies that the truth predicate “is true” does not express any substantial content. To put the point another way, there is complete cognitive equivalence between the left-hand side of the truth schema below and its right-hand side.

• (3) “p” is true if and only if p.

Along this line of thought, on the deflationary conception of truth, there is nothing else to say about truth other than what the truth predicate does, and the truth predicate serves only as a vehicle of generalization, semantic ascent, and certain other logical or expressive functions. As a consequence, truth is not a substantial concept, and so there is no substantial norm of truth independent of the norms of justification.

Now suppose that the above considerations are correct. Then we have no other way but to evaluate whether a belief is true on the basis of our epistemic norms (or reasons) within our conceptual framework. In addition, there is no substantial norm of truth independent of the norms of justification. Then the following questions arise: how should we understand knowledge? And how can we determine whether a person knows that p? The main goal of this paper is to answer these questions. In particular, I will offer a new account of knowledge which explains knowledge in terms of objectively justified belief.

There are important similarities between my account of knowledge and Keith Lehrer’s defeasibility account (1969; 2000; 2003; 2005). On the latter, we can understand knowledge as undefeated justified belief.² But this account faces many serious problems. One important problem is that from one’s subjective point of view, one can hardly bridge the gap between one’s personal justification and objective truth. Another important problem is that this account can hardly accommodate the externalist intuition that the epistemic status of a belief is not entirely determined by factors that are internal to the subject’s perspective. As we will see, however, my alternative account of knowledge can deal successfully with these problems.

In addition to the defeasibility approach, there are other competing approaches to knowledge, such as the causal approach (e.g., Goldman, 1967, 1976), the reliabilist approach (e.g., Goldman, 1986), and the virtue-theoretic approach (e.g., Sosa, 2007). But I will not discuss those competing approaches in this paper for the following reasons. The main goal of this paper is to offer a new account of knowledge which is similar to Lehrer’s account of knowledge. And a proper discussion of other competing approaches would take me too far afield from the main goal of this paper.

This paper proceeds as follows. In Sect. 2, I briefly discuss Lehrer’s defeasibility account of knowledge. As we will see, although there are important similarities between his account and mine, there are important differences as well. In Sect. 3, on the basis of a Sellarsian social practice theory of justification, I argue that knowledge can be understood as objectively justified belief. Finally, in Sect. 4, I argue that my account of knowledge can deal successfully with the problems of Lehrer’s defeasibility account.

2 Lehrer’s Defeasibility Account of Knowledge

According to Lehrer’s defeasibility account, knowledge is undefeated justified true belief. And he understands justification in accordance with his coherence theory of justification. Thus, let me briefly explain his theory.

To begin with, what is coherence? Coherence is usually understood as a matter of how the components in a system of beliefs fit together or dovetail with each other. Except for this sort of metaphorical characterization, however, there is no generally accepted definition of coherence. In this frustrating situation, Lehrer offers us a very illuminating account of this elusive concept. On his proposal, we can understand coherence in terms of “answering all objections” or “beating all competitors.” On this view, one’s belief that p coheres with one’s evaluation system just in case one can answer all objections raised against it on the basis of one’s evaluation system (see Lehrer, 2000, p. 170). In addition, on Lehrer’s view, justification consists of two levels. The first level is personal justification, and the second level is undefeated justification. A subject, S, is personally justified in believing that p just in case she can answer all objections raised against it on the basis of her evaluation system. And “undefeated justification is personal justification that is not based on error” (Lehrer, 2000, p. 153).

At this point, it is important to note that even undefeated justification is based on personal justification. This means that Lehrer adopts a subjective model of justification. Based on this subjective model of justification, he defines knowledge as follows. S knows that p just in case the following four conditions hold:

• (i) It is true that p.

• (ii) S believes that p.

• (iii) S is personally justified in believing that p.

• (iv) S is justified in believing that p in a way that is undefeated.³

One important thing to note about this account is that the fourth condition of knowledge (that is, the no-defeater condition) makes the first condition (that is, the truth condition) superfluous. The reason is straightforward. Suppose that S is personally justified in believing that p on the basis of evidence e. Then this justification is defeated if there is a true proposition d such that the conjunction of e and d fails to justify S in believing that p. And if “p” happens to be false, there is a true proposition d (namely, “not-p”) that defeats the justified status of S’s belief that p. This is because the conjunction of e and not-p fails to justify S’s belief that that p (see Lehrer, 2000, pp. 171–172). But we can hardly rule out the possibility that any given (contingent) proposition might turn out to be false, no matter how strongly it is currently justified. If so, how can one’s personal justification of a belief be connected with truth in a way that yields knowledge? To put the question another way, how can one bridge the gap between one’s personal justification and objective truth?

Lehrer addresses the above question by appealing to what he calls “the principle of trustworthiness”:

T. I am trustworthy (worthy of my own trust) in what I accept with the objective of accepting something just in case it is true. (Lehrer, 2000, p. 138)

On Lehrer’s view, S is personally justified in believing that p just in case she can answer all objections raised against it on the basis of her evaluation system. And S can answer an objection raised against her belief that p if it is more reasonable for her to accept that p than the objection. But her belief that p will not be truth-conducive if she is not trustworthy in judging this kind of comparative reasonableness. Therefore, to meet objections, S has to accept the principle of trustworthiness (see Lehrer, 2005, p. 421). How then does Lehrer defend this principle?

On his view, one’s being justified in holding a belief depends on principle T. As a consequence, one cannot justify T on the basis of one’s evaluation system. For this reason, Lehrer admits that T applies to itself. If, however, T applies to itself, then the justification of T would be circular. Nonetheless, Lehrer argues that the circularity involved in the justification of T is virtuous, rather than being vicious. Besides, he argues that the circularity involved in the justification of T is explanatory, rather than being argumentative (see Lehrer, 2000, p. 143).

However, Richard Manning (2003) argues that Lehrer’s retreat from justification to explanation fails in the context of defending T. One important reason is this. Every explanation consists of two distinct components: the explanandum and the explanans. And when we are trying to explain something, we begin with the assumption that that thing needs to be explained. Thus, as Manning (2003, p. 208) points out, in the context of explaining something, we start with the assumption that we can take the explanandum for granted. As a consequence, we can explain why it is reasonable to accept T on the basis of the truth of T, insofar as we can take the explanandum for granted. If so, the explanandum in question, namely, that it is reasonable to accept T, must already have a positive justificatory status. For this reason, when Lehrer retreats from circular justification to circular explanation, he must start by assuming what needs to be justified. In other words, what needs to be justified is assumed as the explanandum, that is, something which we can take for granted. According to Manning, this is not just changing a strategy for the game we have been playing for the purpose of justifying T but rather changing the game itself. The reason is straightforward. If the reasonableness of T were something that can be taken for granted, Lehrer would not have faced the demand for justifying T in the first place.

Despite the above objection, Lehrer (2003, pp. 343–344) still wants to defend T in the following way. If one does not accept T, one can explain nothing. This would be an epistemic disaster. By contrast, if one accepts T, one can explain why one is reasonable to accept many things about which one deeply cares. And it is certainly better to explain as much as one can than to explain nothing. Therefore, this kind of explanatory power makes the circularity involved in T virtuous. But this line of argument amounts to the “this or nothing” argument. And one important problem with this argument is that it does not give us any illuminating insight as to why principle T is correct. In addition, even if it is granted that there are only two alternatives, accepting T and facing an epistemic disaster, it does not follow that T is more likely to be true than the skeptical consequence. The latter could be equally likely to be true. For these reasons, I agree with Manning that Lehrer is not successful in justifying T.

There is another reason why from one’s subjective point of view one can hardly bridge the gap between one’s personal justification and objective truth. On Lehrer’s view, undefeated justification is personal justification that is not based on any error. How then can one determine whether one’s personal justification is not based on any error? Lehrer addresses this question by appealing to what he calls “ultrasystem.” The ultrasystem of a person is what remains when everything false is eliminated from the person’s evaluation system. And a person’s justification of a belief is undefeated just in case the belief is justified on the basis of his ultrasystem. But then, how can a person be in a position to judge that his justification of a belief is based on the ultrasystem? In this regard, Lehrer writes:

One might worry that the ultracritic in the ultra justification game imagined above is merely a useless fiction because no one will actually be in a position to play the role of the ultracritic. The objection is, however, unwarranted. I may know enough about what another person accepts to play the winning role of an ultracritic against him. (Lehrer, 2000, p. 162)

The above reply is implausible, however. Suppose that S’s personal justification for believing that p is undefeated throughout her entire life. Note that this is compatible with the possibility that defeating evidence might be available only after S’s death. In such a case, someone can be in a position to play the role of the ultracritic only after S dies. This means that during her lifetime, S is not in a position to judge that her personal justification for believing that p is based on an error.

Let me sum up the main points made above. Lehrer is not successful in justifying the principle of trustworthiness. In addition, even if a person’s belief is undefeated throughout her entire life, the possibility that the belief might be defeated by contrary evidence available in the future is still epistemologically significant. For these reasons, there remains an important gap between one’s personal justification and objective truth. But Lehrer fails to explain how his account of knowledge can bridge the gap.

There is a related problem. On Lehrer’s defeasibility account of knowledge, S knows that p only if she is justified in believing that p in a way that is undefeated. Thus, S is in a position to claim that she knows that p only if she is in a position to claim that the no-defeater condition holds. As pointed out before, however, even the case that S’s personal justification for believing that p is undefeated throughout her entire life is compatible with the possibility that it is still based on an overriding error. As a consequence, from her subjective point of view, S can hardly be in a position to claim that the no-defeater condition holds. Then she can hardly be in a position to claim that she knows that p, either. But this does not agree with the fact that we are often allowed to make various knowledge claims, such as that we know that the earth goes around the sun.⁴

One more important problem with Lehrer’s account is related to the externalist intuition that the epistemic status of a belief is not entirely determined by factors internal to the subject’s perspective. For example, suppose that in a normal situation a child forms a perceptual belief that an apple is in front of him, on the basis of his reliable perceptual mechanism. Suppose also that this child is unable to offer any suitable justification for this belief because he is not yet epistemologically sophisticated. Even in such a case, it seems, the child knows that an apple is in front of him. Our epistemic goal is usually understood as having true beliefs and avoiding false beliefs. Thus, a justified belief must be truth-conducive. The child’s belief in question was formed by his reliable perceptual mechanism to the effect that it is truth-conducive. Thus, according to reliabilists, true beliefs can amount to genuine knowledge even when the candidate knower is unable to offer any suitable justification. Following Robert Brandom (2000, p. 97), let us call this the founding insight of reliabilism. But Lehrer’s defeasibility account of knowledge can hardly accommodate this insight. He writes:

The evaluation system of the person provides justification for what a person accepts by providing answers to some objections and neutralization of others. … But what is essential is that the person understands how to meet and neutralize the objections to what he accepts. (Lehrer, 2000, pp. 200-201)

But the aforementioned child would not be able to meet the demand for justifying his belief in question because he is not yet epistemologically sophisticated. Hence, Lehrer’s account can hardly explain why the child can be regarded as knowing that an apple is in front of him.

3 Objectively Justified Belief

In this section, on the basis of a Sellarsian coherence theory of justification, I offer an alternative account of knowledge, according to which knowledge can be understood as objectively justified belief. I have defended a Sellarsian coherence theory in detail elsewhere (see Lee, 2017, 2021). Thus, let me here confine myself to briefly explaining this theory.

To begin with, I accept a Lehrerean conception of coherence. As pointed out in the previous section, Lehrer explains coherentist justification in terms of answering all objections. On this view, one is justified in believing that p just in case one can answer all objections raised against it on the basis of one’s evaluation system. But I accept a Sellarsian social practice theory of justification. On this theory, our concept of justification has been developed on the basis of our social practices of demanding justification and responding to such demands (or giving and asking for reasons). Thus, our concept of justification should be understood in accordance with this social practice model of justification. Accordingly, Lehrer’s conception of coherence should be modified in accordance with this intersubjective model of justification. On this intersubjective model, we are justified in believing that p just in case we can answer all objections raised against it in our social practice of justification.

In addition, my Sellarsian social practice theory employs a dynamic model of justification rather than a static model. Let me explain. Our assessments of justification are relative to evidence available to us, and contrary evidence might be available only in the future. Thus, a belief which is currently taken to be justified could lose its positive justificatory status later. For example, Newtonian mechanics was once taken to be justified, but it is no longer justified. For another example, Einstein’s relativity theory is currently taken to be justified. But we cannot completely rule out the possibility that a future scientist could come along and refute this theory with compelling evidence to the contrary. Thus, even a belief which is currently taken to be justified could lose its positive justificatory status later if strong contrary evidence becomes available in the future. Therefore, we should distinguish between being merely taken to be justified and being really (or objectively) justified.

Moreover, the notion of a genuinely alternative conceptual scheme is unintelligible in our epistemic discourse for the following reasons. We have no other way but to meet any demand for justification on the basis of our social practice of justification. Who then are we in our social practice of justification? It is a regulative ideal of our epistemological pursuit that any rational being is not excluded from our justification practices. If any rational being provides us with compelling evidence against our belief that p, we ought to give up the belief for the sake of achieving our epistemic goal of having true beliefs and avoiding false beliefs. In this sense, there are no membership restrictions to our social practice of justification to the effect that any rational being could, in principle, participate in our social practice of justification. Even the future generations are not excluded from this membership. Thus, if our current justification for a belief is based on an overriding error, then some rational being could, in principle, point out the error to us someday, and so the belief could thereby lose its positive justificatory status in our social practice of justification. If, on the other hand, our current justification for a belief is not based on any overriding error, then its positive justificatory status would not be lost in our forever ongoing, dynamic practice of justification. In the latter case, we may say that it is not merely taken to be justified but really justified. Along these lines, we can argue that if a belief has a positive justificatory status in our social practice of justification and if its justification does not depend on any overriding error and so its positive justificatory status will not be lost in the future, then it is not merely taken to be justified but rather it is really justified.

Here, I do not deny that there can be internally consistent but mutually inconsistent belief systems, subjectively or temporally. But it should be noted that such mutually inconsistent beliefs can be subject to rational criticism in our forever ongoing, dynamic practice of justification. For example, if a certain belief of yours is challenged with overriding contrary evidence, then you as a rational believer ought to give up the belief. More importantly, I deny the possibility that a belief is really justified in our forever ongoing, dynamic practice of justification, and yet, its contradictory belief might be equally justified in some alien conceptual framework. Suppose that our belief that p is really justified in our social practice of justification due to the fact that its positive justificatory status does not depend on any overriding error. Under this condition, consider the possibility that its contradictory belief “ ~ p” is equally really justified in some alien conceptual framework. If “ ~ p” is equally justified in this way, there must be some reason R for believing that ~ p. Now, suppose that we can construe R as a reason for believing that ~ p. But this condition conflicts with our first supposition that we are really justified in believing that p in our social practice of justification. This is because R would refute our justification for believing that p. This time, suppose that we cannot construe R as a reason for believing that ~ p. Then we have no grounds for taking R as a reason for believing that ~ p. In this regard, it is important to recognize that anything which we cannot, even in principle, construe as a reason for believing a proposition is simply unintelligible in our epistemic discourse. Therefore, as Donald Davidson (1984) argues, the notion of a genuinely alternative conceptual scheme does not make sense to us.⁵ If this is correct, as Wilfrid Sellars (1963) insists, the best we can do for our epistemic end is to gradually improve our conceptual framework so as to maximize its explanatory coherence, especially to the effect that unexplained events are minimized and successful predictions are maximized.

What then is an objectively justified belief? Can we say, for example, that our belief that the earth goes around the sun is really (or objectively) justified? Currently, this belief has a positive justificatory status in our social practice of justification. Admittedly, we cannot rule out the possibility that its justification might depend on an overriding error. Nevertheless, considering an overwhelming amount of evidence for the belief, this is an extremely unlikely possibility. Thus, as we expect, suppose that there is no defeating evidence which we are omitting or neglecting for this belief. Then it follows that this belief is really justified. Therefore, on the basis of the overwhelming evidence, we can make a fallible claim that our belief that the earth goes around the sun is really justified. And insofar as this fallible claim, as a matter of fact, is not based on any overriding error, we are really justified in believing that the earth goes around the sun. In this sense, fallibility is compatible with being really (or objectively) justified. As pointed out before, we cannot completely rule out the possibility that the justification of a belief might depend on an error. But this does not imply that it is in fact based on an error.⁶ Along these lines, we can understand objective justification as a special kind of intersubjective justification.

Now, with the above point in mind, compare the following three statements:

• (4) We are objectively justified in believing that p.

• (5) We are objectively justified in believing that “p” is true.

• (6) It is objectively true that p.

If (4) holds, then (5) also holds due to the truth schema mentioned in Sect. 1. And there is no epistemically significant difference between (5) and (6). Let me explain. Suppose that our belief that p is objectively justified, and so its positive justificatory status will not be lost in our forever ongoing, dynamic practice of justification. Now, recall that truth is not a substantial concept, and so there is no substantial norm of truth independent of the norms of justification. Accordingly, we have no other way but to evaluate whether “p” is true on the basis of our norms of justification. Besides, if we are justified in asserting that p in our social practice of justification, we are also justified in asserting that “p” is true. Therefore, if our belief that p does not lose its positive justificatory status in our forever ongoing, dynamic practice of justification, then there are no circumstances in which we can rightly claim that “p” is not true. To put it another way, if our belief that p is objectively justified, the possibility that there might be defeating evidence against the belief is not epistemologically significant. Therefore, on my Sellarsian coherence theory, truth is not an external characteristic of objective justification. Along these lines, we can argue that there is no epistemically significant difference between (5) and (6). If this is correct, we can understand objective truth in terms of objective justification.

If the above considerations are on the right track, we can claim that S knows that p just in case we can claim the following three:

• (i) It is true that p.

• (ii) S believes that p.

• (iii) S is justified in believing that p.

The above three conditions are similar to the traditional tripartite account of knowledge. But the first and third conditions should be understood in terms of my Sellarsian social practice theory of justification combined with the deflationary conception of truth.

Let us first consider the third condition of knowledge, namely, the justification condition. As mentioned before, on my account, we are justified in believing that p just in case we can answer all objections raised against it in our social practice of justification. And we should evaluate condition (iii) in accordance with this intersubjective model of justification. As an illustration, consider a Gettier case (see Gettier, 1963). Suppose that, as far as Smith can remember, Jones has always owned a Ford, and recently Smith got a ride in a Ford Jones claimed was his. Thus, on the basis of this evidence, Smith believes the following proposition:

• (7) Jones owns a Ford.

In addition, on the basis of (7), Smith also believes (8):

• (8) Either Jones owns a Ford or Brown is in Barcelona.

But Jones sold his old Ford, and the Ford Jones currently drives is a rental car. Nonetheless, (8) is still true, because Brown is in Barcelona by mere coincidence. In this case, Smith is not blameworthy for believing (8). Nevertheless, we cannot say that he knows (8), because his belief in (8) is true merely by luck. And my account provides a proper explanation about why Smith fails to know (8). Let me explain.

In the above case, Smith believes (7) on the grounds that as far as he can remember, Jones has always owned a Ford and, recently, he got a ride in a Ford Jones claimed as his own. However, there is defeating evidence, namely, that the Ford Jones currently drives is in fact a rental car. Here, the reason why Smith is not blameworthy for believing (8) is that the defeating evidence is not available to him. Nevertheless, the defeating evidence can be available to us, and so we can put forth the defeating evidence to Smith. In that case, Smith’s justification for (8) is undermined by the defeating evidence. His belief in (8) is based on (7) which he is no longer justified in holding. And the fact that (8) happens to be true has nothing to do with Smith’s evidence for believing (8). Therefore, although Smith’s belief in (8) could be taken to be justified before the defeating evidence is available to us, he is not really justified in believing (8). Hence, Smith does not know (8), because the third condition of knowledge is not satisfied.

Let us now turn to the truth condition on knowledge. I endorse the deflationary conception of truth. On this conception of truth, truth is not a substantial concept, and so there is no substantial norm of truth independent of the norms of justification. As a consequence, the justification condition on knowledge makes the truth condition redundant for the following reason. Suppose that we are justified in denying that “p” is true. Then it is implied that we have evidence which defeats S’s justification for believing that p. Thus, if we can deny that “p” is true, we can also deny that S is intersubjectively justified in believing that p. This means that if we can endorse that S is intersubjectively justified in believing that p, we can also endorse that “p” is true. What then is the role of the truth condition? It plays an expressive role: by saying that “p” is true, we can express explicitly that we agree with S’s belief that p.

4 Important Merits of My Account

In this section, I argue that my account of knowledge can deal successfully with the problems with Lehrer’s defeasibility account.

The most important problem of the defeasibility account is that from one’s subjective point of view, one can hardly bridge the gap between one’s personal justification and objective truth. In this regard, it is worth recalling that even if S’s belief that p is undefeated throughout her entire life, the possibility that defeating evidence might be available only after her death is still epistemologically significant. But my Sellarsian social practice theory of justification can cope with this epistemic limitation.

As argued in the previous section, if our belief that p has a positive justificatory status in our social practice of justification and if its justification does not depend on any overriding error and so its positive justificatory status will not be lost in our forever ongoing, dynamic practice of justification, then it is not merely taken to be justified, but rather it is objectively justified. In such a case, the possibility that there might be defeating evidence against the belief is not epistemologically significant. In other words, we can distinguish between what is merely taken to be justified and what is objectively justified by recourse to our forever ongoing, dynamic practice of justification. In addition, as also argued in the previous section, we can understand objective truth in terms of objective justification. Therefore, my Sellarsian social practice account can bridge the gap between intersubjective justification and objective truth (or objective justification) by recourse to our forever ongoing, dynamic practice of justification.

We may put the matter this way. Unlike the case of Lehrer’s subjective coherence theory, my Sellarsian social practice theory of justification can meet the following objection: the fact that we have done everything to reach the truth in our social practice of justification is compatible with the possibility that contrary evidence might be available in the future. As pointed out before, the future generations are not excluded from our forever ongoing, dynamic practice of justification. As a consequence, if our belief that p currently has a positive justificatory status in our social practice of justification and if its justification does not depend on any overriding error and so its positive justificatory status will not be lost in our forever ongoing, dynamic practice of justification, then this belief is objectively justified, rather than merely being taken to be justified. Hence, we can meet the above objection by appealing to our forever ongoing, dynamic practice of justification.⁷

Another important thing to note is that we have, at least in principle, no real difficult in evaluating the justification condition in the context of our social practice of justification. Let me explain. As previously pointed out, on my account, we can claim that S knows that p just in case we can claim the following three:

• (i) It is true that p.

• (ii) S believes that p.

• (iii) S is justified in believing that p.

And condition (iii) should be evaluated in accordance with the aforementioned social practice model of justification and so in terms of our epistemic norms which have a positive justificatory status in our social practice of justification. As a consequence, if we can say that S believes that p in a way that does not violate any of our epistemic norms, we can also say that condition (iii) holds. Therefore, when we evaluate the justification condition in the context of our social practice of justification, we have, at least in principle, no real difficulty in evaluating this condition.

Of course, one’s knowledge attribution is fallible so that we cannot rule out the possibility that it might turn out to be false in the future. But at any point in time, we have no real difficulty in evaluating the aforementioned three conditions of knowledge attributions. In particular, as pointed out before, if we are justified in believing that p in our social practice of justification, and if S believes that p in a way that does not violate any of our epistemic norms, we can say that condition (iii) holds. And insofar it is reasonable for us to say so, it is also reasonable for us to say that S knows that p. In addition, as also pointed out before, the fallibility of such an epistemic evaluation is compatible with the case that S is objectively (or really) justified in believing that p. In other words, we can claim that our belief that p is objectively justified, without ruling out the possibility that it might turn out to be false. For example, we can make a fallible claim that we are objectively justified in believing that the earth goes around the sun. For this reason, in order to endorse the justification condition, we don’t have to rule out the possibility that this endorsement might be defeated someday. In this regard, it might be worth emphasizing that my Sellarsian social practice account can appeal to the social division of epistemic labor. Hence, we can make a fallible knowledge claim, such as that we know that the earth goes around the sun. And it is reasonable for us to make such a knowledge claim until and unless we are given positive reasons to doubt it.

As pointed out in Sect. 2, another important problem with Lehrer’s account is that it can hardly accommodate the founding insight of reliabilism. By contrast, my account of knowledge can accommodate this insight. Consider the following epistemic principle:

• EP₁: Our perceptual judgments are generally reliable.

My Sellarsian coherence theory can defend EP₁. Since I have defended this claim in detail elsewhere (Lee, 2021), let me here confine myself to briefly explaining its main idea.

On this theory, it is inevitable to address any justification question on the basis of our social practice of justification. EP₁ is no exception, for it is a rational question whether or not EP₁ is correct (or justified). In addition, our social practice of justification requires the default-and-challenge structure of justification. The reasons are roughly as follows. In the first place, the infinite regress of justification is not possible in our social practice of justification. In the second place, as mentioned in Sect. 1, genuine doubts are possible only against a background of beliefs that are not doubted at the same time; to put the point another way, there must be a conceptual framework within which doubts and settlement of doubt can take place. Therefore, the possibility of one’s defending something requires that some claims be treated as having default justification unless we are given positive reasons to doubt them; that is, there must be some claims for which the burden of proof (or justification) shifts to any challenger.

With the above points in mind, consider again whether EP₁ is justified. As pointed out before, we can engage in a rational debate about whether EP₁ is justified; and we have no other way but to meet this demand for justification on the basis of our social practice of justification; moreover, EP₁ is justified just in case all objections raised against it can be met in our social practice of justification. Thus, if someone raises a legitimate objection to EP₁ in our social practice of justification, it can be successfully challenged. But insofar as EP₁ is not successfully challenged in this way, it can be defended roughly on the following grounds: EP₁ has so far been successfully served as an epistemic principle in our social practice of justification. And we have no positive reason to believe that EP₁ is incorrect or defective. As a consequence, as far as we know, there is no better alternative principle to replace EP₁ for rationally pursuing our epistemic goal. If these conditions hold, then we can take EP₁ as having a default positive justificatory status in our social practice of justification, and so we can shift the burden of proof to any challenger. In this way, we can defend EP₁ without falling into a vicious regress of justification. Let me elaborate on this point a bit further.

As pointed out above, our social practice of justification requires the default-and-challenge structure of justification. In addition, our epistemic goal includes having true beliefs about the world around us. Moreover, it is a minimum presumption for our epistemic discourse that it is reasonable for us to pursue our epistemic goal. Now, as far as we can judge on the basis of our current conceptual framework, we ultimately obtain information about the world through our senses. In other words, our senses are the ultimate sources of information about the world. Thus, if we could not rely on our perceptual abilities in order to obtain information about the world, then we could not realize our epistemic goal. In this regard, it should be noted that denying the general reliability of our perceptual abilities is tantamount to closing our ultimate epistemic door to the world. Therefore, if we rejected the general reliability of our perceptual judgments, we could not get our epistemic pursuit off the ground. Along these lines, we can argue that we have no better alternative to replace EP₁ for rationally pursuing our epistemic goal, until and unless we are given positive reasons to think otherwise. If so, we can defend EP₁ as enjoying a default positive justificatory status in our social practice of justification. In other words, it is reasonable for us to accept EP₁, until and unless we are given positive reasons for not doing so. Another important thing to note about my social practice model of justification is that it is not required of every subject that the subject alone should be able to answer all objections in order to be justified. We can engage in the social division of epistemic labor on the matter of meeting objections.

As argued above, we can take EP₁ as enjoying a default positive justificatory status in our social practice of justification. For this reason, my account of knowledge can accommodate the founding insight of reliabilism. Consider again the aforementioned case in which a child has an ordinary perceptual belief that there is an apple in front of him. In this case, the child himself does not have to justify EP₁. As a member of our society, he can rely on the social division of epistemic labor, so that he can defer to some relevant experts in our society on the matter of justifying EP₁. Along these lines, we can argue that a child’s perceptual belief that there is an apple in front of him has a default positive justificatory status in our social practice of justification. As a consequence, unless some challenger provides us with positive reasons to doubt this belief, we can say that the child knows that there is an apple in front of him. It is in this way that my account of knowledge can accommodate the founding insight of reliabilism.

Another thing worth noting is that my account of knowledge does not amount to the “this or nothing” argument. As argued in the previous section, on my account, we can understand objective truth in terms of objective justification, which can, in turn, be understood as a special kind of intersubjective justification. In addition, as also pointed out before, it is a minimum presumption for our epistemic discourse that it is reasonable for us to pursue our epistemic goal. To deny this presumption is tantamount to denying our nature as rational believers. Even the skeptic can hardly deny this presumption to rationally defend his skeptical claim. Accordingly, we can shift the burden of proof for this fundamental epistemic presumption to the skeptic. To put the point another way, it is reasonable for us to pursue our epistemic goal, until and unless the skeptic somehow shows that our epistemic endeavors are futile. Therefore, insofar as it is reasonable for us to hold the minimum epistemic presumption, we can claim that our beliefs such as that the earth goes around the sun are objectively justified or that we know that the earth goes around the sun. Hence, my account of knowledge explains the conditions under which we can make such a knowledge claim. In addition, we can meet the demand for justifying EP₁ on the basis of my Sellarsian coherence theory as well. As argued before, we can take EP₁ as enjoying a default positive justificatory status in our social practice of justification. Therefore, we can defend EP₁ until and unless this epistemic principle is successfully challenged with good reasons.⁸

5 Concluding Remarks

In this paper, I argued that knowledge can be understood as objectively justified belief. On my account, we can understand the justification condition in accordance with a Sellarsian social practice model of justification; and on the basis of this intersubjective and dynamic model of justification, we can overcome the problems with Lehrer’s defeasibility account of knowledge, which is based on a subjective model of justification.

Above all, my account can cope with the most important problem with the defeasibility account, namely, that from one’s subjective point of view, one can hardly bridge the gap between one’s personal justification and objective truth. In this regard, it is important to recall the key difference between Lehrer’s defeasibility account of knowledge and my account. Even if S’s belief that p is undefeated throughout her entire life, the possibility that defeating evidence might be available only after her death is still epistemologically significant. By contrast, my Sellarsian social practice theory of justification can cope with this epistemic limitation. If our belief that p has a positive justificatory status in our social practice of justification and if its justification does not depend on any overriding error and so its positive justificatory status will not be lost in our forever ongoing, dynamic practice of justification, then it is objectively justified. In such a case, the possibility that there might be defeating evidence against the belief is not epistemologically significant. Therefore, my Sellarsian social practice theory can bridge the gap between intersubjective justification and objective truth (or objective justification) by recourse to our forever ongoing, dynamic practice of justification. In this regard, it is worth emphasizing that my account can overcome the epistemic limitation of Lehrer’s subjective model of justification by recourse to the social division of epistemic labor. Moreover, unlike Lehrer’s view, my account does not rely on any problematic principle like the principle of trustworthiness.

Another important merit of my account is that it can also accommodate the externalist intuition that the epistemic status of a belief is not entirely determined by factors that are internal to the subject’s perspective. In this connection, it should be noted that my coherence theory is distinguished from standard internalist views. This is because this intersubjective model of justification allows us to take into consideration evidence that might not be available to the subject.

For these reasons, my account of knowledge, which is based on an intersubjective and dynamic model of justification, is much more plausible than Lehrer’s defeasibility account, which is based on a subjective model of justification.⁹