Can propositional beliefs (belief about the truth or falsehood of a that P statement) be held without it influencing behavior? It’s difficult to say whether a belief is really a belief if it doesn’t change behavior, or if beliefs, by their very nature, necessarily change behavior. I think one can argue that a belief is more justified if it changes behavior in a particular way. That is what I’ll discuss here.

Propositional Knowledge (that P) is of two different kinds: knowledge that corresponds to external, mind-independent reality and knowledge of agreed upon concepts. The former is what science and ontology is concerned with and the latter is what culture and art is concerned with. An example of the first kind would be that it was overcast outside when I arrived at work and an example of the second kind would be that it was overcast in Mordor when Frodo arrives at Mount Doom. The difference should be obvious: the former reports something that occurred outside of human minds while the latter is fantasy. Of course, the mind-dependent knowledge isn’t necessarily only about fantasy – it could also be considered knowledge that it is wrong to engage in incestuous relationships. While there is good reason to hold such a belief (eg accumulation of recessive alleles in progeny), it is only true because minds believe it to be true; one can conceive of a world where minds did not believe this and therefore ‘that incest is wrong’ would be untrue.

Both types of knowledge are subject to different kinds of justification criteria.

Justifications for mind-independent knowledge:
a) if the truth were otherwise, one would not believe it.
b) if it can be used to make accurate predictions about future states of affairs.

Justifications for mind-dependent knowledge:
a) if enough people hold the same belief at one time.
b) if it is useful for obtaining social goals.

Functionalism says there is no belief unless it influences a person’s actions. This is a priori to even belief, meaning it must also be necessary for Justified True Belief (JTB). This is where the second (b) justifications come into play in the above analysis of JTB for the two sorts of propositional knowledge.

For mind-independent knowledge, (a) is simply (what I believe to be) the best justification for JTB of propositional knowledge qua knowledge. But (b) takes the functionalist way of thinking about JTB. If my belief has an effect on my behavior, it is true because I was able to generate accurate predictions about future states of affairs. My belief that it’s raining right now is true if it causes me to predict that: if and only if I take my umbrella with me outside, then I will stay dry; I took my umbrella with me and because I did, I stayed dry.

For mind-dependent knowledge, (a) is essentially the definition of what mind-dependent knowledge is. However, (b) takes the functionalist way of thinking about JTB in that by agreeing with these beliefs, I am able to achieve social goals. Those goals could be anything from having a coherent conversation about something (certain things must be agreed upon by all parties to a conversation in order for it to be coherent) all the way to obtaining money or social status.