Wednesday, February 09, 2011

Aquinas: Why There Is an Immaterial Soul


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I. The Text, from Summa theologiae I.75.1c: "Whether the soul is a body."


I answer that, to seek the nature of the soul, we must premise that the soul is defined as the first principle of life of those things which live: for we call living things "animate," [i.e. having a soul], and those things which have no life, "inanimate." Now life is shown principally by two actions, knowledge and movement. The philosophers of old, not being able to rise above their imagination, supposed that the principle of these actions was something corporeal: for they asserted that only bodies were real things; and that what is not corporeal is nothing: hence they maintained that the soul is something corporeal. This opinion can be proved to be false in many ways; but we shall make use of only one proof, based on universal and certain principles, which shows clearly that the soul is not a body.It is manifest that not every principle of vital action is a soul, for then the eye would be a soul, as it is a principle of vision; and the same might be applied to the other instruments of the soul: but it is the "first" principle of life, which we call the soul. Now, though a body may be a principle of life, as the heart is a principle of life in an animal, yet nothing corporeal can be the first principle of life. For it is clear that to be a principle of life, or to be a living thing, does not belong to a body due [merely] to the fact that it is a body; since, if that were the case, every body would be a living thing, or a principle of life. Therefore a body is competent to be a living thing or even a principle of life, as "such" a body [i.e., a specific kind of body]. Now that it is actually such a body, it owes to some principle which is called its act. Therefore the soul, which is the first principle of life, is not a body, but the act of a body; thus heat, which is the principle of calefaction, is not a body, but an act of a body.


II. Aquinas' Argument in Syllogistic Form:

Major: The first principle or formal cause of life of those things which live cannot be corporeal (No M is P).
Minor: The soul (anima) is the first principle of life of those things which live (S is M).
Conclusion: Therefore, the soul is not corporeal (No S is P).         

Proof of the Major: Although a body may be a principle or formal cause of life, as the heart is a principle of life in an animal, it cannot be the first principle of life.  For it is clear that to be a principle of life, or to be a living thing, does not belong to a body due [merely] to the fact that it is a body; since, if that were the case, every body would be a living thing, or a principle of life.  Therefore a body is competent to be a living thing or even a principle of life, as "such" a body [i.e., a specific kind of body].  Now that it is actually such a body, it owes to some principle which is called its act (form); thus heat, which is the principle of calefaction, is not a body, but an act (form) of a body.

Proof on the Minor: This is the definition of 'soul'. Explanation"... principle of life": Life is shown principally by two actions, knowledge and movement; now, we call these things (that exhibit knowledge and movement) "animate" (animata) [i.e. having a soul], and those things which do not, "inanimate" (inanimata).  "First principle...": It is manifest that not every principle of vital action is a soul (for then the eye would be a soul, as it is a principle of vision; and the same might be applied to the other instruments of the soul) but it is the "first" principle of life, which we call the soul.  Therefore, the first principle of life is the soul.  

And the conclusion follows: The soul is incorporeal; it is not a body, but the first act (or substantial form) of any living body.

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