Reasons vs. Causes
• Reasons tell us why we ought to believe (do) something. Causes tell us why we in fact do believe (do something).
• Reasons are normative, causes are factual.
• Reasons justify, causes explain.
(Caution: the terms here are imprecise, and we use terms such as ‘explanation’ or ‘reason’ in different ways than just outlined.)
Example. Suppose I say: “I believe that there are no triangles.” You say “Why do you believe that?” You can be either asking for the cause of my belief or (more likely in this case) for my reasons for believing it.
Suppose that you are interested in the explanation of why (as a matter of fact) I hold the belief. I may tell you (truthfully) that I hold this belief because my father told me so (perhaps kept saying so), so I kind of have come to hold the belief by default, as it were. In doing so I make no pretense to argue that this is a reason – I may in fact believe that my father holds many false beliefs. I am only claiming that as a matter of fact this is how I came to believe that there are no triangles. I’ve told you what the cause is, not what my reasons are.
Suppose that you are interested in the justification of my belief. You want to know why a(ny) rational person should think that there are no triangles. Prima facie, you might add, there are reasons to believe quite the contrary. Look around you – there are triangles everywhere. And, you might cinch your argument by drawing one like that: There is at least one triangle. This one (you point). And you can draw others . . . So, triangles exist! (Here is what I will say to you and what I will say to you will provide a reason for my believing that there are no triangles:) The problem is that no matter how perfect your triangle might appear, it never will conform to the standards of geometrical definition of a triangle. The sides of this triangle are not fragments of a straight line (if you look closely, the segments will turn out not to be “straight” at all