Some key terms and distinctions

1. Some key terms and distinctions

2. A Priori vs. A Posteriori • If I know something, I must have justification. • If justification essentially relies on sensory experience, then it is a posteriori justification and my knowledge is a posteriori knowledge. • Examples of such knowledge are: • It is raining (I see it is). • It was snowing yesterday (I remember seeing it.) • It is raining in New York (my brother can see it and tells me it is.) • In the second case, the sensory information is recalled by a reliable memory; in the third, transmitted by a reliable witness. • If I know something essentially through reason, then my justification is a priori justification and my knowledge is a priori. Examples of such knowledge are: • 2+2=4 • The area of a triangle is ½ x base x height.

3. What do the terms mean? • A posteriori means afterwards – think of posterior – and a priori means before – think of prior. • Intuitively - a priori knowledge: ‘before’ applying my senses. I can prove something is true all ‘in my mind’. • When I have a posteriori knowledge, I need to apply my senses. • (N.B. I need to use my powers of reason as well. If I see it is raining, then my senses deliver information to my mind but it is reason that concludes it is raining through applying the concept rain.) • A crude way of thinking about the distinction. A priori knowledge is ‘armchair knowledge’. A posteriori knowledge is ‘in the field knowledge’. You have to get up and look or listen or smell or taste or feel – you need to gather evidence.

4. Necessary and Contingent • This is a distinction between facts or states of affairs. • Something is necessary if it could not have been otherwise. • It is a necessary truth that bachelors are unmarried and that triangle have three sides. There is no scenario or possible world in which things could have been otherwise. • Something is contingent if it could have been otherwise. • It is actually a matter of fact that war broke out in 1914 and that Paul Sheehy exists. However, the world could have been such that there was no WW1 and no Paul Sheehy. • To that something is a necessary truth is to say that it is true in all possible worlds. • Something is contingently true if true in at least one possible world.

6. Rationalism maintains that knowledge of reality is a priori. • Rationalism claims that reason allows us to know necessary truths ranging from mathematics to ethics to metaphysics. • The necessary truths are not just tautologies, but tell us about the nature of reality: • what exists and what it is really like. • Reason provides the foundation of general principles or truths on which detailed scientific enquiry can be based.