7.3.3 The Fallible Nature of Justification

The sources of beliefs are varied. Perception, reason, hope, faith, and wishful thinking can all result in belief. Yet just because something results in belief, that does not mean that the belief is justified. Beliefs that result from wishful thinking are not justified because wishful thinking does not make a belief more likely to be true. A source of justification is a reliable basis for belief. Yet while justification is a reliable source, notice that this does not mean that the belief is true; it just makes it more likely. Justified beliefs can turn out to be false. In order to drive this point home, we will briefly look at four different sources of belief. As you will see, each source is fallible.

One source of belief is memory. Memory is not always reliable. First of all, that you do not remember something in your past does not mean that it did not happen. Second, when you do remember something, does that guarantee that it happened the way you remember it? Because people can misremember, philosophers distinguish between remembering and seeming to remember. When you actually remember P, then this justifies believing P. When you seem to remember P, this does not justify believing P. The problem is that remembering and seeming to remember often feel the same to the person trying to remember.

Most beliefs are the product of inference. When you use reason to come to belief, the justification you have is inferential; hence, inferential justification is equivalent to logical justification. But as discussed in the chapter on logic, not all forms of inference can guarantee truth. Inductive reasoning, which is the most common source of beliefs, is only probable even when done well. Furthermore, people often make mistakes in reasoning. Just because someone reasoned their way to a belief doesn’t mean they reasoned well. But assume for a moment that a person comes to a belief using deductive reasoning, which can guarantee truth, and they reason well. Is it still possible that their belief is false? Yes. Deductive reasoning takes as its input other beliefs to then derive conclusions. In good inductive reasoning, if the premises are true (the input beliefs), then the conclusion is true. If the input beliefs are false, then even good deductive reasoning cannot guarantee true beliefs.

Another source of belief is testimony. When you gain beliefs based on the stated beliefs of others, you rely on testimony. Testimony is usually considered something that happens only in a court of law, but in philosophy, the term testimony is used much more broadly. Testimony is any utterance, spoken or written, occurring in normal communication conditions. Instances of testimony include news magazines, nonfiction books, personal blogs, professors’ lectures, and opinions volunteered in casual conversation. Often, testimony is a reliable source of information and so can be justified. When you form beliefs based on the testimony of experts, it is justified. But even when justified, those beliefs could be false because experts are vulnerable to all of the weaknesses of justification covered in this section. More will be said about testimony in the section on social epistemology.

Last, perception can be used as a source of justification. Perception includes the information received from the senses (smell, taste, touch, sight, hearing). People often automatically form beliefs based on perception. However, not all beliefs that follow from perception are guaranteed to be true, as the possibility of knowledge by acquaintance shows. As discussed earlier, Russell maintained that the only automatically justified beliefs gained from perception are about the existence of sense data (Russell 1948). When looking at the bird outside of my office window, I only have knowledge by acquaintance of the experience of seeing the bird on a branch in my visual field. I know that it seems to me that there’s a bird. But how do I get from those sense data to the justified belief that there really is bird on the branch? I must rely on another belief about the reliability of my perception—a belief that I can only get by inference, specifically induction. I reason from past instances where I believe my perception is reliable to the general belief that it is reliable. And of course, induction is fallible. Whenever one moves from knowledge by acquaintance to further beliefs—such as the belief that sense data is caused by actually existing objects—there is room for error.

Not all philosophers agree that all perceptual beliefs are mediated through sense data (Crane and French 2021). The view called direct realism states that people have direct access to objects in the external world via perception. While direct realism holds that one can directly perceive the external world, it still cannot guarantee that beliefs about it are true, for both hallucinations and illusions are still possible. Figure 7.7 is an example of an illusion.

If you focus only on the top two lines, it appears as though they are of different lengths. Yet the bottom two lines indicate that this appearance is illusory—the lines are actually of equal length. Illusions function as evidence that perception sometimes misrepresents reality. Even direct realists have to contend with the possibility that beliefs gained through sense perception could be wrong. Hence, sources of beliefs, even when they are usually justified, are nevertheless fallible. The possibility that the subject could be wrong is what gives rise to philosophical skepticism—the view that knowledge in some or all domains is impossible.