[Note: This is an excerpt (pp. 98-108) from chapter V of Skepticism and the Veil of Perception. ©2001 Michael Huemer. Do not reproduce without permission of the publisher. --mh]

3. A Principle of Foundational Justification

My theory is a version of foundationalism. Foundationalism says that there are certain beliefs, the so-called "foundational beliefs," which we are justified in holding and which do not depend on any other beliefs for their justification. Perceptual beliefs, in my view, are foundational. Notice that the definition of foundational beliefs does not say that they do not depend on anything else for their justification; it says they do not depend on other beliefs for their justification. In my view, perceptual beliefs certainly do depend on something else for their justification: namely, perceptual experiences.

As we mentioned earlier (section II.1), foundationalists must explain what differentiates foundational beliefs from merely arbitrary beliefs. They must state a condition or set of conditions under which a person has foundational (noninferential) justification for believing a proposition. A "principle of foundational justification" is a principle identifying such a condition. A foundationalist might put forward any number of principles of foundational justification, to account for different kinds of foundational beliefs. I believe, however, that a single principle of foundational justification can account for all foundational beliefs.(1) The principle is what I call the rule of Phenomenal Conservatism (PC) (this is using "phenomenal" in the sense of "pertaining to appearances," not in the sense of "fantastic"):

(PC) If it seems to S as if P, then S thereby has at least prima facie justification for believing that P.

In the remainder of this section, I explain what that means.

First, note that its seeming to S as if P is a distinct state from S's believing that P.(2) This is important, since otherwise PC would be granting foundational justification, automatically, to all beliefs, and this is not what we want; we want to identify a special class of foundational beliefs, to be distinguished from merely arbitrary beliefs.

One kind of seeming-as-if state is perceptual, and the argument showing this state to be different from belief was that it is possible for it to seem to you as if P, even when you do not believe that P; in fact, even when you know that ~P.(3) There are also other, nonperceptual seemings, that is, cases in which its seeming to you as if P is not an aspect of your perceptual experience. There are memory-related seemings:(4) for example, I seem to remember that Saturn is the fifth planet from the sun. The argument showing this to be different from belief parallels the argument in the perceptual case: we can easily imagine a case in which it seems to me as if P in just this way but in which I do not trust my memory and so do not believe that P. (The argument would be at least as strong for experiential memory as it is for factual memory.) Likewise, there are intellectual seemings: when I think abstractly about the proposition, "The shortest path between any two points is a straight line," it seems to me to be true. Philosophers commonly call these intellectual seemings "intuitions." Intuitions can be distinguished from beliefs by means of the same kind of argument we have used above: it is possible for a person to have the intuitive sense that P but not to trust his own intuitions, and so to not believe that P. As a case in point, consider the intuitively obvious proposition, "In a plane containing a line and a point not on the line, there exists exactly one line parallel to the given line passing through the given point." There are some physicists who say that this proposition, as obvious as it seems, is false. Nor do these scientists lack the intuitions the rest of us (and the rest of the mathematicians and scientists in history) have. They admit that the proposition seems obviously true, but they say that our intuitions on this matter are not to be trusted and that there is powerful empirical evidence against it. (I refer, of course, to the non-Euclidean geometry used in Einstein's general theory of relativity.) The point here, as in the earlier examples, is not whether the scientists are reasonable to make this judgement, but simply that it is possible to make such a judgement. This suffices to show that its seeming to one, intellectually, that P is different from one's believing that P.

Next, we consider the notion of prima facie justification.(5) When a belief is said to be prima facie justified, two things are meant: first, that the belief does not depend on other beliefs for its justification, and second, that the belief's justification can be defeated by countervailing evidence. In other words, prima facie justification is both foundational and defeasible. Now, many people feel this combination of properties to be paradoxical, but it really is not. Compare the legal concept of the presumption of innocence: the defendant is presumed innocent, until proven guilty. This means that the defense need not present evidence proving the defendant's innocence (though they may do so, of course). If no proof is brought forward during the trial, neither of the defendant's innocence nor of his guilt, then the defendant is acquitted. But of course, this does not mean that a defendant can never be convicted. If the prosecution brings forward enough positive evidence that the defendant is guilty, then the presumption of innocence is overcome and the defendant is convicted.

Prima facie justification in epistemology works similarly. According to phenomenal conservatism, the epistemological default position is to accept things as they appear. The appearances are presumed true, until proven false. That means that when it seems as if P and no evidence emerges contravening P, it is reasonable to accept P. (Since, as I claim, phenomenal conservatism is the sole principle of foundational justification, "evidence against P" would consist of other things that seem to be the case and that, directly or indirectly, either contradict or render it improbable that P.) But that does not mean that P can never be refuted, of course; it is possible that sufficient evidence will emerge against P to overcome its presumption. Prima facie justification only provides us with an initial starting point; it does not guarantee that we have to end up where we started.

For a concrete example, take the Müller-Lyer illusion (figure 5.1).

The top line appears to be longer than the bottom line, so other things being equal, you would be reasonable in thinking that the top line is longer. However, you can get out a ruler and measure these lines. If you do this, you will find them to be of the same length. At that point, it would be reasonable for you to revise the initial belief and conclude that the lines are really of the same length. This is because you know that measurement is generally a more reliable way of determining lengths than just eyeballing things. Of course, your new belief, that the lines are of equal length, is also based on how things seem, including what you seemed to see when you were measuring the lines; there is no (rational) way around that. It is just that you rightly take the latter seemings to be more reliable. As to why we take measurement to be more reliable than unaided visual length-estimates, I think this is partly a matter of past experience (beliefs based on measurements tend to exhibit fewer and less serious conflicts with each other and with other beliefs than unaided visual estimates) and partly due to the fact that measurement relies on situations in which what seems to be the case is particularly clear and unambiguous--which, of course, is the point of measurement procedures. This example shows that we normally treat perceptual beliefs as having just the sort of presumption of truth that phenomenal conservatism attributes to them.

Now why do I say, in my statement of PC, that S has "at least" prima facie justification? Well, I don't want to rule out the possibility of cases in which S would have incorrigible justification for believing that P. That is, I want to allow that there may be (as in fact I think there are) cases in which S has justification for believing P not dependent on other beliefs, and in which this justification cannot be defeated by further evidence. An example would be my present belief that for every number x, (x + 1) is greater than x. I think I am not only justified in believing that, but furthermore, no future evidence could disconfirm it. Similarly, suppose I have a splitting headache. At this time, it seems to me that I am in pain, and I believe I am in pain. Again, I think my belief that I am in pain is not only justified, but justified in a way that is immune from countervailing considerations.

Those examples were not examples of perceptual beliefs, of course. I do not believe there are any examples of perceptual beliefs that have incorrigible justification. But I intend phenomenal conservatism to be a general principle of foundational justification. It explains not only why perceptual beliefs are noninferentially justified, but also why any other belief that is noninferentially justified is such. And this is important, for it means that my account of perceptual knowledge does not depend upon ad hoc principles of justification contrived specially to let in knowledge of the external world; I propose to account for perceptual knowledge by the same general principle I apply to all other kinds of knowledge. This should make my account more persuasive for those who are skeptical about perceptual knowledge but who allow knowledge of other kinds (that is, external world skeptics).

Notice that phenomenal conservatism does not hold that from the proposition, "It seems to me as if P" one may infer P. That would be a principle of inferential justification. What makes you justified in believing P, under PC, is not that you believe or know that it seems to you as if P, and you thereupon get to conclude that P; rather, it is the mere fact that it does seem to you as if P that makes you prima facie justified in believing P. Thus, to satisfy the antecedent of PC one does not need to have any beliefs--one does not even need to have the concept of an appearance, nor the concept of justification. In the case of perceptual beliefs, it is our perceptual experiences themselves--and not our assessments of, or beliefs about them--that justify our initial beliefs about the external world.

Even so, however, note that I am not saying a perceptual belief, or any other kind of foundational belief, cannot be supported by other beliefs. I am saying it need not be supported by other beliefs. These are two quite different things. Foundational beliefs are defined to be beliefs that do not depend upon other beliefs for their justification; they are not defined as beliefs that are not supported by other beliefs.(6) To return to the legal analogy: the presumption of innocence in a criminal trial means that the defense is not required to give positive evidence of the defendant's innocence. It does not mean the defense is prohibited from giving positive evidence of the defendant's innocence. If they have such evidence to give, all the better for them. So there could arise a case in which the defendant's acquittal was overdetermined: suppose the prosecution failed to prove the defendant's guilt, and, in addition, the defense was able to prove his innocence. There is certainly no contradiction in that, and in that case, there would simply be two conditions, each sufficient for acquitting the defendant. Likewise, there can be cases in which a belief has two kinds of justification, both a foundational one and an inferential one.

Incidentally, this is more than a merely theoretical possibility. There are many cases in which a belief has both kinds of justification. Suppose, for instance, that I see a red ball on the table. I am foundationally justified in believing that there is a red sphere there, due to the character of my perceptual experience. You happen to be in the same room with me, and I ask you, "Do you see a red sphere there?" whereupon you answer, "Yes." This gives me a second, inferential justification for thinking there is a red sphere there.(7) Obviously, the existence of this second justification does not remove or change the character of the original, noninferential one.

Lastly, notice that phenomenal conservatism does not assert, as a general rule, "If it seems to someone as if P, then P." If it did, phenomenal conservatism would be false, for there are many cases in which it seems as if P but P is not the case. Nor does phenomenal conservatism assert or imply, "Most of the time, when it seems as if P, P is true." The latter is true, but it just is not what PC is about. Phenomenal conservatism is epistemological, not metaphysical. It says that when it seems as if P and there is no evidence to the contrary, it is reasonable to believe P. Compare the legal presumption of innocence again: the principle is not that defendants in general are innocent; it is not even that most defendants are innocent (in fact, quite the reverse is the case). Rather, it is the normative principle that if the prosecution fails to prove the defendant's guilt, he should be acquitted.

A corollary is that phenomenal conservatism is a necessary truth, not a contingent one. There is no possible world in which phenomenal conservatism is false, although there are possible worlds in which most of the things that appear to be so are not so. Recall the brain-in-a-vat scenario. If you were a brain in a vat, then most of the things that seemed to you to be the case would in fact not be the case. Nevertheless, it would still be reasonable for you to believe those things, given your situation, and given that you would have no evidence of your being a brain in a vat. The diabolical scientists stimulating your brain make it so you have a bunch of false beliefs, but they do not make it so you have unjustified beliefs; in fact, their method of getting you to adopt the false beliefs is precisely to give you justification for them.

4. In Defense of Phenomenal Conservatism

Why should we accept my proposed principle of foundational justification? I claim that PC is self-evident, once it is seen in its proper light. To see it in its proper light, we have to remind ourselves of two things. The first is that the notion of "justification" we are talking about is internalist, rather than externalist. That is, we are talking about what propositions are justified from the subject's own point of view. Thus, if P were false, but there were no way that S could reasonably be expected to guess that, then its falsity would have no bearing on S's justification for believing P in the internalist sense. What is "unjustified" in the internalist sense is what one could be blamed for believing.(8)

The second thing we must remember is that the notion of justification we are concerned with is epistemic (rather than, e.g., prudential or moral). Epistemic justification is the kind of justification that is assessed from the standpoint of the pursuit of the truth and the aversion to error. The relation between justification and truth is like the relation between expected utility and utility; that is, the acceptance of (only) justified propositions is what constitutes the rational pursuit of the truth.

Now consider an account of rationality offered by Richard Foley: "A decision is rational as long as it apparently does an acceptably good job of satisfying your goals."(9) This is plausible. Notice the need for the qualifier, "apparently." In order for a decision to be rational, it is not necessary that it in fact will satisfy your goals. A rational person can be mistaken about what will satisfy his goals, in which case he will do the thing that it appears to him will satisfy his goals rather than the thing that actually will. To return to my example from chapter II: it would have been irrational for the fisherman to just throw the pearl back into the ocean--even though that action would in fact have satisfied his goals better than keeping the pearl.

Now, if my goal is to have true beliefs and avoid having false ones, and if P seems to me to be true, while I have no evidence against P, then from my own point of view, it would make sense to accept P. Obviously, believing P in this situation will appear to satisfy my epistemic goals of believing truths and avoiding error better than either denying P or suspending judgement.

Another thing that will help to bring the self-evidence of PC into focus is reflection on the way you actually do form beliefs (omitting the cases of self-deception and leaps of faith, which are cases of epistemically irrational belief). When you are conscientiously seeking to know, you weigh a proposition in your mind. What determines whether you accept it or not? Well, in some cases you consider an argument for it. But this will help only if you accept the premises of said argument. How do you decide whether to accept a premise of an argument? You do not, in real life, demand an infinite series of arguments. Rather, you consider the premise on its own: if it is sufficiently obvious (to you) you accept it; otherwise, not. Moreover, it is difficult to imagine what possible alternative a person critical of this procedure could have in mind. Should you, perhaps, accept the propositions that seem false instead? Surely this cannot be rational. Accept all and only the propositions that are in fact true? But acting on this advice is the same thing as accepting the propositions that seem true to you. Imagine I have a child who is having difficulty with fruit names. I tell him to put all the fruits that he takes to be apples into a basket. When he's done, I empty the basket, start over, and tell him this time, put all the fruits that are apples into the basket. From my point of view, I might seem to have said something different, but (leaving aside the implication the child may pick up that he did it wrong the first time, which is not part of the literal meaning of what I said) from the child's perspective I have essentially just repeated the same instruction, and he will obviously just do the same thing.

Or perhaps you should accept nothing at all? But half of your epistemic aim is to gain true beliefs. When P seems to you to be true and there are no grounds for doubting it (no defeaters), what more are you looking for? This is as good as it gets. Why should you withhold belief in P, keeping in mind the internalist sense of "should" (recall section II.6 above)--because it is still possible that P is false? But this seems to be just an extreme and unreasonable bias toward the "avoiding error" part of your epistemic goal, as against the "believing truths" part. You would not let the mere possibility that P is true suffice for you to accept it, so why let the mere possibility that P is false suffice for you not to accept it?

Consider, in fact, the argument you have just read. No doubt some philosophers will accept it, while others will not. Which ones will accept it? The ones to whom it seems correct, of course. Even if you do not accept it, you still will be thinking in accordance with the rule of phenomenal conservatism. The difference will merely be that to you, it does not seem correct. There is no (rational) escape from the reliance on how things strike you. (Even if you decide to rely on the opinions of a reliable expert, you will still be relying on how things seem to you: what the expert seems to you to be saying, and who seems to you to be an honest and reliable source.)

Because of this fact, any attempt to deny the principle of phenomenal conservatism will be self-defeating, for all thought and reasoning presupposes the principle in a certain sense. Even the reasoning put forward by philosophical skeptics, even as they try to present grounds for doubting all appearances, depends for its force on the way things appear to the skeptic and his audience. To illustrate, reconsider the following argument in favor of philosophical skepticism, the infinite regress argument:

Argument A:
1. In order to know anything, I must have an adequate reason for believing it.
2. In order for a reason to be adequate, I must know it to be true.
3. I cannot have an infinite series of reasons.
4. A series of adequate reasons cannot be circular.
5. Therefore, I cannot know anything.(10)

This argument, on the face of it, carries some force. Some work will need to be done to respond to it, to show, in the face of the argument, how we can have knowledge. But now compare the following "argument" for the same conclusion:

Argument B:
1. 3 = 5.
2. Therefore, I cannot know anything.

This "argument" carries no force at all, so that it is not even clear whether it deserves to be considered an argument. This form of skepticism does not call for a response; there is no philosophical work to be done in explaining how knowledge is possible in the face of it. Similarly, consider the following anti-skeptical "argument":

Argument C:
1. There are seventeen inhabited planets in the Andromeda galaxy.
2. If there are seventeen inhabited planets in the Andromeda galaxy, then skepticism is false.
3. Therefore, skepticism is false.

Just as argument B does not call for a response, argument C does not count as a response. Just as we do not need to take argument B seriously, the skeptic does not need to take argument C seriously.

Why? What is the difference between (A) and (B)? The difference is not that (B) has a false premise, for (A) has a false premise too (which one, we will see later). Most of the arguments that have been presented throughout the history of philosophy have contained one or more false premises (for philosophical arguments are almost always logically sound, but their conclusions are usually false). Still, they have not been bad in the way that (B) and (C) are. What we are trying to account for is not why arguments (B) and (C) are unsound, but why (B) and (C) are not serious arguments at all; why do they not have a place in the discussion of philosophical skepticism?

Notice that in a way, this issue is prior to the question of whether philosophical skepticism is true, for unless we (at least implicitly) have a way of distinguishing what counts as a serious argument from what doesn't, we cannot even approach the issue, philosophically. This does not mean the skeptic would win dialectically; it means the practice of dialectic could never get started. We would have no conception of what it would be to motivate skepticism, or anything else.

What is wrong with argument (B) is that, not only does it have a false premise (like most philosophical arguments), but its premise doesn't even appear true; indeed, it seems obviously false. Hence, it doesn't even give us a prima facie reason for doubting that I can have knowledge. Similarly, the premises of (C), while not obviously false, do not particularly seem true either. Hence, we do not take them even prima facie as grounds for thinking I can have knowledge. This is why neither (B) nor (C) requires philosophical discussion or response.

The above illustrates the way in which the rule of phenomenal conservatism is presupposed in the practice of dialectic: what we count prima facie as motivating a position is a matter of what at first seems true. Clearly the intuitively plausible (true-seeming) premises of (A) are taken as prima facie justified; else the argument would give no motivation at all to skepticism. (Also clearly, but less importantly for our present purposes, they are taken as only prima facie justified, or else discussion of the issue would terminate once the validity of the argument was agreed upon.) If phenomenal conservatism is false, then dialectic as we practice it is fundamentally and intrinsically irrational. In calling it "intrinsically" irrational, I mean to imply that the problem would be irremediable; there is nothing that could be recognized as a form of dialectic or reasoning that would not be irrational. As a result, it is impossible coherently to argue against phenomenal conservatism. In engaging in argumentation, one is presupposing that there is a distinction between serious arguments and mere strings of arbitrary statements such as (B) and (C). If phenomenal conservatism is false, we cannot draw this distinction in practice. Thus, the skeptic who would argue against phenomenal conservatism labors at pulling the rug out from under his own feet. And if the skeptic eschews argument altogether, we shall hardly be concerned by our failure to "answer" him.

I think, in fact, that the lesson is even more general than I have just indicated--that is, the rule of phenomenal conservatism underlies not only our practice of argumentation (the attempt to convince others through giving expression to one's reasoning), nor, even, just the practice of reasoning. I think the principle of phenomenal conservatism underlies judgement in general. I think reflection will reveal that all judgement, whether inferential or not, is a process in which one accepts a proposition on the basis of how things seem to oneself. If phenomenal conservatism is false, so that the way things seem to oneself is irrelevant to epistemic justification, then all judgement must be irrational. And this is something which no philosopher, not even a skeptic, can accept.


1. That is, I think the principle accounts, for every foundational belief, for why that belief is justified. Additional principles, or a stronger principle, would be needed to account for the degree of justification each such belief has.

2. Chisholm has observed that "appear" words are sometimes used to express tentative judgements, though I do not think that this refutes my contention here. See chapter IV, note 39.

3. See section IV.4.2-3.

4. The concept of a memory appearance is related to, but distinct from, Shoemaker and Parfit's concept of a "quasi-memory." Quasi-memories are states similar to experiential memories (as distinct from factual memory), except that it is conceptually possible to quasi-remember someone else's experiences (but it is not conceptually possible to quasi-remember things that never happened at all) (Shoemaker, "Persons and their Pasts," 271; Parfit, 14-15). "Memory appearances," on the other hand, are states like memories (experiential or factual), except that it is possible to have a memory appearance of something that is not true or that never happened.

5. A number of foundationalists, probably most foundationalists these days, rely on the notion of prima facie justification. See for example Audi, The Structure of Justification, 307-10; Pollock, Contemporary Theories of Knowledge, 177-78. For the argument that there is nothing inconsistent about this, see Alston, "Has Foundationalism Been Refuted?"

6. Alston makes this point, along with several other important clarificatory ones, in "Has Foundationalism Been Refuted?"

7. There are at least two inferential steps here: first, from the fact that you spoke certain words to the fact that you see, or at least think you see, a red sphere there, and second, from the fact that you see or think you see a red sphere there to the conclusion that there probably is a red sphere there. According to Burge (though I think he is wrong), I would actually have foundational justification for believing that you see the red sphere; however, the second inferential step would still be necessary, even on his theory. Moreover, there is no difficulty in generating any number of examples in which I would have a further, inferential justification for thinking there is a red sphere there.

8. See section II.6.

9. Foley, Working without a Net, 8. I do not know, however, whether Foley would agree with the use to which I have put his theory.

10. This is an abbreviated version of the argument from section II.1.