I.  Metaphysical Distinctions Among Types of Propositions:


Necessary Truth.  A necessary truth is a proposition that could not possibly have been false. This can be expressed by saying that a necessary truth is a proposition that is true in every possible world.  An example of a truth that many philosophers take to be necessary in this sense is:  2+2 = 4.


Contingent Proposition.  A contingent proposition is a proposition that is not necessarily true or necessarily false (i.e., is not the negation of a necessary truth).  A contingent truth is a true proposition that could have been false; a contingent falsehood is a false proposition that could have been true.  This is sometimes expressed by saying that a contingent proposition is one that is true in some possible worlds and not in others.  An example of a contingent proposition is the proposition that human beings have evolved from other forms of life.



II.  Epistemological Distinctions Among Proposition Based on our Method of Determining Whether or Not They are True:


Analytic Truth.  There are in the philosophical literature a variety of characterizations of analyticity.  In the readings, always pay close attention to how the author defines "analytic".  The most common characterization of an analytic truth is that it is a necessary truth that is true in virtue of meaning or that is true because the concept of the subject is included in the concept of the predicate.  Philosophers who claim there are analytic truths have disagreed about which truths are analytic, though they all agree that definitions are themselves analytically true--for example, the following would be held to be an analytic truth:  A brother is a male sibling.


Synthetic Truth.  A truth that is not analytic.  For example:  George W. Bush was president.


A Posteriori Justification/Knowledge:  A proposition is justified/known a posteriori just in case its being justified or known depends, at least in part, on the course of one's experience.  It is common to distinguish inner experience (experience of one's own thoughts and other internal states) from outer experience (experience that at least seems to be of things outside us).  Because experience is itself contingent (it is not necessary that anyone have experience) philosophers who employ the term have taken it for granted that one could not be justified in believing (or know) that a proposition p was necessarily true on the basis of experience. 


Empirical.  The term "empirical" has been used in many different ways.  In one use, it is pretty much interchangeable with a posteriori justified (if justified at all).  In this course, I use it more narrowly to mean a posteriori justified on the basis of outer experience.  This limitation to outer experience is implicit in accounts of empirical evidence that assume that such evidence is publicly accessible and publicly shareable.  It is partly a result of the contrast between phenomenology (where the evidence is largely made up of the results of introspection of one's own mental states—that is, internal experience) and empirical psychology (where the evidence is limited to publicly observable behavior and other publicly observable measurements). 


A Priori Justification/Knowledge.  A priori justification/knowledge is usually defined as justification or knowledge that is not a posteriori--that is, not based on experience.  However, philosophers who use the term use it more restrictively than that definition would indicate.  A priori justification or knowledge is assumed to be based on a purely rational way being justified in believing or in knowing necessary truths as necessarily true.