Subject: Re: Aquinas's Five Ways

Hi Professor Klima,
Please address these concerns regarding St. Thomas Aquinas's Five Ways:
1) Clarify Objection 2 and the rebuttal to it on page 72.  I do not understand what Aquinas means by a "middle term of the demonstration" (72) nor do I understand how it relates to effects, essences, or existence.
2) With an infinity of efficient causes mustn't there be a first efficient cause to perpetuate this infinite train of causes?, i.e. why would there be "no efficient cause" (74) if it was possible for efficient causes to proceed into infinity?
----------------------------------------------------------------------
(1) The middle term of a syllogistic demonstration is that term which is common in both premises of the syllogism, and which is dropped in the conclusion. A syllogism is an inference from two premises that share one term, the middle term. For example, consider the following syllogism:

Every animal is a living body
Every man is an animal
------------------------------
Every man is a living body

In this syllogism the middle term is the term 'animal', which is shared by both premises. This term is dropped in the conclusion, which joins the other terms of the premises, namely, the subject term of the second premise (the so-called minor premise, whence its subject is also called the minor term) and the predicate term of the first premise (the so-called major premise, whence its predicate term is also called the major term).

Aquinas' objection states (on the basis of Aristotle's considerations concerning scientific demonstrations in his Posterior Analytics) that the middle term of such a syllogism in a scientific demonstration has to be the (quidditative definition or some essential predicate signifying) the essence of the thing that the demonstration is about (just as in the demonstration above). But we cannot possibly know the divine essence (since its infinite perfection is incomprehensible by any of our finite concepts); therefore, we cannot form scientific demonstrations about God, and so we cannot prove His existence.

In the reply he points out that not all scientific demonstrations need to meet this strict requirement. In many scientific demonstrations, namely, in those in which we prove the existence of a cause from the existence of its effect, we need not know the essence of the cause, it is enough if we know what its name means. In general, the form of this type of demonstration would be the following:

X is the cause of F
The cause of F exists
---------------------
X exists

where we know that the minor premise is true on the grounds that F (namely, the effect of X) exists. Here we obviously need not know what the essence of X is, it is enough if by X we mean the cause of F. But this is precisely the case in Aquinas' proofs of the existence of God. Since the term 'God' means 'the First Cause', he has in mind the following syllogism:

God is the First Cause (of motion/efficient causation/coming to be and passing away/degrees of perfection/goal-directed behavior)
The First Cause (of all these manifest effects) exists
---------------------------------------------
God exists

The syllogism is so obvious that Thomas does not even explicitly state it in his actual arguments, but rather spends all his efforts on showing the truth of the minor premise.

(2) If the series of causes is infinite, then *in that series* every cause has a prior cause, so *in that series* there is no first cause, i.e., a cause that has no prior cause. This is precisely why it is so important to make clear just what sort of series of causes we need to consider here, because in a series of per accidens, potential causes it is not impossible to go to infinity, and even if in that series we had to stop somewhere, that first cause would definitely not be the actual, universal, per se cause of all being, which is alone the First Cause that we can justifiably call God.
See also
http://www.fordham.edu/gsas/phil/klima/phru1000/AquAns.htm