No true philosopher entertains the slightest doubt that God is not a body, nor the form of a body, nor a complex substance. It would be impossible that God should be a body, seeing that He is the immovable Mover of all things; for one body, unless it first move itself, cannot set another in motion. Again, as spirit is more noble than body, God, were He a body, would not be the noblest of all beings, neither would He be the Supreme Ruler, since the body is governed by the spirit.

We must further hold, that God is not the form of a body, as the soul is the form of the human body; because that which exists of itself is far more noble than that which exists in others. Consequently, as God is the most noble of all things, He must exist in Himself, and not in any body. Again, things composed of matter and of form are more perfect than matter alone and form alone; for the simple reason that the whole is always more perfect than its parts. If, then, God were the form of a body, there would be something more perfect than He; for the combination of matter and form would be more perfect than form alone. It would further follow that God could not act by Himself; since, as form has no being without matter, it cannot operate without matter. Hence, as God would need others for His operations, He would not be the First Cause.

It is, likewise, evident that God is not a complex Being, but Pure Act and Simple Substance; for every complex being depends on others, and composite bodies depend on those that are simple. Since, therefore, God is the First Cause, independent of all others, and the one on whom all things depend, He cannot be a complex Being, but must be Simple Act. Again, were He a complex Substance, He could not be the First Supreme Being in the universe; for complex bodies do not precede their parts, but result from them; and the union of these parts could not take place, had not some first cause preceded them. We must conclude, therefore, that God is Simple Substance and Pure Act.[18]