It is unnecessary to deal specially with each of the many writers who have used from different standpoints the a posteriori form of argument in order to prove the existence of Deity. The objections already stated apply to the whole class; and, although probably each illustration used by the theistic advocate is capable of an elucidation entirely at variance with his argument, the main features of objection are the same. The argument a posteriori is a method of proof in which the premises are composed of some position of existing facts, and the conclusion asserts a position antecedent to those facts. The argument is from given effects to their causes. It is one form of this argument which asserts that man has a moral nature, and from this seeks to deduce the existence of a moral governor. This form has the disadvantage that its premises are illusory. In alleging a moral nature for man, the Theist overlooks the fact that the moral nature of man differs somewhat in each individual, differs considerably in each nation, and differs entirely in some peoples. It is dependent on organization and education: these are influenced by climate, food, and mode of life. If the argument from man's nature could demonstrate anything, it would prove a murdering God for the murderer, a lascivious God for the licentious man, a dishonest God for the thief, and so through the various phases of human inclination. The a priori arguments are methods of proof in which the matter of the premises exists in the order of conception antecedently to that of the conclusion. The argument is from cause to effect. Among the prominent Theistic advocates relying upon the a priori argument in England are Dr. Samuel Clarke, the Rev. Moses Lowman, and William Gillespie. As this last gentleman condemns his predecessors for having utterly failed to demonstrate God's existence, and as his own treatise on the "Necessary Existence of God" comes to us certified by the praise of Lord Brougham and the approval of Sir William Hamilton, it is to Mr. William Gillespie that the reader shall be directed.
The propositions are first stated entirely, so that Mr. Gillespie may not complain of misrepresentation:
1. Infinity of extension is necessarily existing.
2. Infinity of extension is necessarily indivisible. Corollary.—Infinity of extension is necessarily immovable.
3. There is necessarily a being of infinity of extension.
4. The being of infinity of extension is necessarily of unity and simplicity.
Sub-proposition.—The material universe is finite in extension.
5. There is necessarily but one being of infinity of expansion.
Part 2, Proposition 1.—Infinity of duration is necessarily existing.
2. Infinity of duration is necessarily indivisible. Corollary.—Infinity of duration is necessarily immovable.