Some Important Distinctions

1.  Two Kinds of Knowledge

•        a priori =_def  does not depend for its authority upon the evidence of experience or testimony, that which is presupposed and known by reflection apart from experience (compare the geometry lessons in the Meno).

                            Example:    Nothing can both be and not be.  (Russell, 88)

•        a posteriori =_def  depends for its authority upon the evidence of experience

                            Example:    There are people in this room right now.

2.  Two Kinds of Statements

•        analytic =_def  true or false in virtue of the meaning of the words alone

                                    (so, the opposite would be contradictory)

                            Example:    "A giraffe is a long-necked animal."  (See also Russell, 82)

•        synthetic =_def  not true or false in virtue of the meaning of the words alone

                                   (so, the opposite would not be contradictory)

                            Example:    "Tame tigers growl."

3.  Two Kinds of Existence (also, by extension, truths)

•        necessary =_def  it could not be the case that it does not exist; a statement that is true "in all possible worlds"
  

                            Example:    God  (very controversial); the number 2;
                                              the statement "2 + 3 = 5"

•        contingent =_def  it could be the case that it does not exist; a statement that is imaginably false, i.e., not true in all possible worlds

                            Example:    Human beings;
                                              the statements "Bush is President", "Phillips has gray hair."

4.  Some Combinations

•        synthetic a priori  (Kant, disputed by Russell)

                            Examples:    mathematics and geometry  (7 + 5 = 12)

•        necessary a posteriori  (Kripke)

                            Examples:   some scientific discoveries (Water is H₂O.)