The fundamental principle in the fourth way

The fundamental principle in the fourth way is that whatever is most such in any order is the cause of all things in that order. St. Thomas picked fire as an example, but in other places he also gave the example of a seed being caused by a tree, or an animal being the cause of the semen with which it generates- i.e. that which is most fully this particular tree is a cause of that which is a particular tree in an imperfect or potential manner. That there is another sense in which this seed is the cause of this tree is also evident, but to say this is beside the point and changes nothing. The general principle one is supposed to get from the example of the seeds is that what potentially has some completion (and all potential is potential for some completion) has to receive the completion from something else. To deny this principle of the fourth way is the same as saying that something is able to receive what it already has; i.e. that something is able to become what it already is; i.e. that something already is what it is not.   


  1. oohlah said,

    February 21, 2007 at 8:40 pm

    I agree with your understanding of the fundamental principle of the fourth way, but my question for you is: according to Aquinas, is “completion” essential existence?

    In other places, e.g., Summa Theologica, Ia. iv. 2, ad 3, Aquinas concludes that God is “essential existence himself.” Other things, that is “merely existing things,” are less perfect to a certain degree because they share in existence though they do not share in every mode of existence. Only God is that which is every mode of existence.

  2. a thomist said,

    February 21, 2007 at 9:26 pm

    To your first question:

    I am not sure if this is an objection, and I am not sure of what direct relation you are trying to draw either to the fourth way or to my explanation of it. “Completion” as I am using it here is the same as perfection (I’ve blogged on this before- St. Thomas does not use the word “completion” but I take it as an English synonym for the Latin “perfectum” and it is futher a synonym for the English word “perfection” if the words are spoken of per se). Perfection is what St. Thomas calls “act” as opposed to potency, and every act is also a perfection. But existence is understood as act and perfection, in fact, it is the act of all act and the perfection of all perfections.

    So I would say that Aquinas calls existence a kind of completion as I am using the word here.

    As to your second paragraph, if you are saying that God contains all perfections, I agree. To say he has all modes of existence is strange to me- to exist contingently is a mode of existence, in the sense of being a way some things exist.

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