The words "rational" and "irrational" are commonly used to describe a person's beliefs or a person's cognitive state. It is often claimed by agnostics and atheists that religious belief is irrational, or at any rate, not rational. It is important to recognize the different senses that can be given to "rationality." Here I summarize three main types. We will develop and examine them more closely as the course moves forward, as well as their relation to the related cognitive state of knowledge.

This outline is a supplement to Handout I, Rational and Irrational Belief

1. Epistemic Rationality: A belief B (or cognitive state) is epistemically rational just if a person's holding B is in some sense relevantly related to the goal of believing what is true and not believing what is false. "Epistemic" refers to knowledge, or - as in this case - the goal of knowledge, the acquisition of true beliefs. The relationship between rationality and knowledge will be discussed later. But there is a close connection between knowledge and epistemic rationality because of the common epistemic goal or truth directedness.
2. Non-Epistemic Rationality: A belief B (or cognitive state) is rational in the non-epistemic sense just if a person's holding B is in some sense relevantly related to non-truth oriented goals of human life. For instance, there is means-end rationality, the sort of rationality that attaches to the actions when they are appropriate or effective to teach some goal. By example, if I want keep my car in good working condition, it would be means-end irrational to never put oil in it, refuse to get it serviced, etc.

A. INTERNAL RATIONALITY [IR]: Some proposition p seems to you to be true and you lack good or sufficient reason to suppose that p is not true or that your grounds for believing p are inadequate.

Good or sufficient reasons for supposing that some proposition p is not true (or that your grounds for believing p are inadequate) are called defeaters. The conception of [IR] is based on a principle of reason, called the principle of credulity, according to which, in the absence of special considerations (i.e., defeaters), if something seems to you to be such and such, then probably it is such and such, so it rational to believe it.

For failures of [IR], see cases #3 (possibly), #4, and #5 on Handout I.

Variations on [IR] relative to the defeater clause:

1. Some proposition p seems true to you and you are not aware that you have a defeater for p.
2. Some proposition p seems true to you, you have a defeater, but you are not aware that you have a defeater (but you would be aware of it if you reflected on matters a bit).
3. Some proposition p seems to be true to you, you have a defeater for p, and you recognize that you have a defeater a defeater for p.

B. DEONTOLOGICAL RATIONALITY [DR]: P seems true to you and there is no relevant evidence that you ought to have that would give you a defeater for your belief that p, and whatever evidence you have for p was not acquired by violating any intellectual duties.

We are all familiar with the idea of "duty" and "obligation" in ethics or moral philosophy. We say that Johnny ought to do X or ought not to do Y. We are entitled/permitted or not to act or behave a certain way depending on whether our action does not contravene any of the relevant (moral, legal, or prudential) norms or rules. The deontological view of rationality (sometimes also called justification, see Handout IV) suggests that there are similar norms for our cognitive life, specifically regarding what things we believe or do not believe. We might call these epistemic duties or intellectual obligations. If we return to the notion of the epistemic point of view, we will discover that acquiring true beliefs and avoiding false beliefs serves as the guide for determining epistemic duties and obligations. These could include refraining from believing in the absence of sufficient evidence, accepting those propositions that we see follow from (or are rendered probable by) some other proposition(s), or not accepting those propositions for which we have sufficient reason to think are false.

Internal rationality and deontological rationality are closely related. A belief will be internally irrational if you have a defeater for it, and it might be thought that the reason why is because do believe anything for which you have a defeater runs contrary to the epistemic point of view. Of course, internal rationality simply says, if you have a defeater, then your belief isn't rational. The deontological conception is a bit more complex. A belief will be deontological irrational if there are reasons you ought to have (but in fact don't) that would constitute a defeater for your belief, or if the evidence you have for your belief was acquired because you violated some intellectual duty.

For failures of [DR], see cases #11, #13, and #14 on Handout I. Cases #3, #4, and #5 may also represent failures of deontological rationality.

C. PROPER FUNCTION RATIONALITY [PR]: P seems true to you and your belief that p was produced by properly functioning (and unimpeded) truth-aimed, cognitive faculties.

We are all familiar with idea of "proper function." Things have different sorts of functions. It is the function of a computer to run the programs installed on it (e.g., Microsoft Word, Outlook Express), and these programs have functions too (e.g., to compose written documents, correspond with people). It is the function of a CD to play music when placed into a CD player. A computer will not function properly with a virus, nor will a CD with function properly when played if it has deep scratches on it. An eye subjected to very bright light, or an ear subjected to very loud noise, will fail to function properly (at least for as time). Conversely, a thing that is functioning properly will be functioning according to a certain design plan, specifications for how the thing should work. It will do these things only if it is free from malfunction, dysfunction, or impedance.

The idea behind proper function rationality is that your cognitive faculties also have a design plan. There is a way they should function when they are functioning properly, and there are unfortunate results when they malfunction. Now it certainly seems that at least some of our cognitive faculties have as their purpose or design the production of true beliefs. Since we are concerned with epistemic rationality, proper function rationality will be related to the proper functioning of truth-aimed cognitive faculties (e.g., sense experience, reason, memory, etc). Like deontological rationality, there is a normativity here, but it is the normativity of proper function not obligation. There is a certain way your cognitive faculties or belief producing processes should function if they are to be successful in the goal of acquiring true beliefs and avoiding false ones. An irrational belief, in this sense, will be a belief that is formed by cognitive faculties that are either (i) truth-aimed but not functioning properly or (ii) properly functioning but not truth-aimed (but aimed at something else, like survival).

For failures of [PR], see Handout I, cases #3, #10, #12, and possibly cases #4 and #5.

Notice that according to each of the views of rational belief (above), it possible to hold a rational false belief and an irrational true belief. Hence, rationality is distinct from truth. Note this in the cases on Handout I.

Rational false belief: #1, #9

Irrational true belief: #5, #10, #14, and possibly #12.

When discussing whether religious belief is rational or not, it is crucial that one ask what sense of rationality is being denied to religious belief. Secondly, there is the question about which of these sorts of rationality is more desirable (where they represent genuine options). These will be among the questions that we investigate later in the course.