Cecilia asked:

Aristotle and Thomas Aquinas had a similar way of reasoning but with a different focus: Aristotle
based all his theory on reason, and Thomas Aquinas based his theory on God. Can you give me
deeper similarities and differences between the two?

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In a soundbite, it is fair to say that Aquinas tried to make the philosophy of Aristotle compatible with
Christianity in the same way that St Augustine brought the philosophy of Plato into Christian thought.
Aquinas holds that there is no reason for supposing a conflict between what we can learn from the
philosophical life and what is taught by Christian revelation. The idea is that we can reason ourselves
to the truths that we can find in the Bible.

Aquinas, following Aristotle, maintains that God is wholly simple and thus timeless, spaceless and
bodiless. This wholly simple God is the God of Catholic Theology. Aristotle's position presumes the
existence of a God as an efficient cause which set the natural processes of the world in motion. God
is also a final cause in that he gives the universe its meaning. This Aquinas accepts; but because
Aristotle lived a long time before the death of Christ, Aquinas adds that we must rely on the Bible and
Jesus' teachings for a more developed picture of what God is like.

Aquinas tries to prove the existence of God on an Aristotelian basis in the first three of his Five Ways.
These arguments are essentially cosmological arguments — and they presuppose Aristotle's view of
causation (the idea of final causes) and Aristotle's laws of motion which states that movement is a
potentialitywithin an object (by contrast with Newton's view that forces act on objects to cause
movement.) The Unmoved Mover is what starts the chain of motion — where the chain of causes and
effects comes to an end.

Curiously, however Aristotle came to a conclusion that there may be either forty-seven or fifty-five
unmoved movers.

The other important similarity surrounds the idea of natural law: to Aristotle things in the world have
fixed essences and their function is to fulfill as well as possible what is fixed by this nature. Man's
natural proclivity according to Aristotle is eudaimonia— happiness — and for the Christian Aquinas
this leads to the beatific vision of God. Both philosophers believe in these natural inclinations. Laws
are natural to the extent that they relate to what humanity is; if they are a true reflection of the world
then we must examine humanity to know what humankind ought to do. According to Aquinas, rules
and principles help humanity realise their natural inclinations. Rational agents see the importance of
these rules for the good flourishing of society.

This involves reasoning from the factthat humans are x to a conclusion concerning valuesviz. that
humans ought to do y. Hume pointed out that this is not an inference one can make. The difficulty is
implicitly escaped by Aristotle and Aquinas by the thought that 'ought' is a way of saying that one is
teleologically seeking to be a good human being — reason finds natural goals.

A weakness with the position is that it assumes that there is one goal for everybody; the fact/value
inference remains questionable, as do the scientific doctrines upon which the argument is based.
Many people think that it is illegitimate to think that the universe cannot be uncaused, but that God
alone can be.

Adam Gatward