The presupposition I want to consider first is Aquinas's explicit statement of the only basis he thinks he really needs, now that he is about to start the new investigation. And it's interesting that the basis he cites is not an explicitly existential claim. Instead, he merely ascribes to the subject of his investigation a single characteristic, the one associated particularly with argument G2: 'let us take as a starting-point (principium) that which is already manifest from the above [arguments]—I mean, that God is altogether immovable' (14.119). Since by 'altogether immovable' (omnino
immobilis) he means incapable of being changed in any way,
10 This may be seen in the variants of this claim used as premisses in later chapters: 'altogether without motion' (15.122); 'altogether impassible and immutable' (16.132; cf. 23.215 and 217). The claim itself is invoked in e.g. 15.121, 17.138, 19.152, 20.156, 23.215.
there's nothing unmistakably divine about this characteristic. As we saw in examining G2, some of its argumentation does offer good grounds for denying mutability to anything that, like Alpha, could count as an ultimate explanation of change. But I think it's in any case self-evident that Alpha can count as the ultimate explanation of change only if it is itself altogether unchangeable in at least the aspect of it that is supposed to account for all change. We'll be seeing more of this immutability, but for now it seems right to say that following Aquinas in taking the absolute immutability of the ultimate explanatory principle as an already established starting-point for the investigation of Alpha's nature does not involve either accepting an existence ii claim or associating with Alpha a characteristic that only God could have.
11 Aquinas does open ch. 14 with an announcement of an existential result: 'Therefore, having shown that there is a first being (est aliquod primum ens), ... we have to investigate its characteristics' (14.116). But I think it's clear that this particular existence claim is important to him only as an announcement that he has fulfilled the Aristotelian pre-condition for going on to investigate the nature of the first being that is his science's subject. What makes me think it's clear is that at the end of ch. 14 it is only immutability, not existence, that he deliberately cites as the basis from which to go on.
In the order in which I'm considering them, the second of chapter 14's end p.90
Kretzmann, Norman , (deceased) formerly Susan Linn Sage Professor Emeritus of Philosophy, Cornell University, New York
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