This chapter covers the classical forms of the ontological argument for the existence of God by AnseIm and Descartes. Two modern forms by Malcolm and Plantinga are also discussed. The arguments are then evaluated in respect of their strengths and weaknesses and the extent to which they can be considered a proof for God.
a) A priori and a posteriori
Key question How do we decide the truth value of a premise?
As we saw in chapter 1 (p. 5), identifying the type of argument (that is, deciding if it is deductive or inductive) does not, in itself, prove whether the conclusion is true or false. We must also decide whether the individual premises are true or false. Types of argument merely tell you about the logical connection between the premises and the conclusion. How then do we decide about the truth value of the premises? Consider the following premise: Charles gains a grade A at AS Religious Studies.
Key word A posteriori: from or after
experience.
How do I go about finding out if that is true? I would have to go and check it out in some way — maybe look at a list of published results or ask to see Charles' certificate from the exam board. I cannot assume that Charles has a grade A at AS Religious Studies. I would need to make some kind of investigation. I could only conclude the truth value in the light of some experience (for example, seeing the certificate). If this is the case then the premise is said to be a posteriori (after experience). Some premises may be such that their truth value can be decided without reference to experience. Consider the following premise: The circle is square.