The second of the Newtonian laws of motion warns us that all physical tendencies to motion work themselves out concurrently and instantaneously as tendencies. St Thomas's reasoning however is beset with this difficulty, that, parted from the body, the soul, on his showing, still retains a physical tendency to union with the body: is there any more difficulty, anything of greater violence, in a soul having to wait for its first union with the body than in its having to wait, as it certainly does wait for centuries, for its reunion in the resurrection?
The two telling arguments against the pre-existence of souls are, first, that pace Platonis et Origenis it is wholly unproved; secondly, that a spirit, that had once existed free, would suffer violence by becoming the 'form' of a body under conditions of mortality.
There are those who venture to think, although St Thomas does not think so, that while the soul in the body is properly called an 'incomplete substance,' -- for otherwise it would not be the 'form of the body,' -- yet, parted from the body, it expands into the completeness of pure intelligence, and has no 'natural craving' for union with the body any more. Resurrection then is not within the purview of philosophy, as it is not the fulfilment of any natural exigence; and, at least in the resurrection of the just, the soul shall be in the body on quite other conditions than those under which she now dwells in this prison-house of flesh. But of this in the fourth Book.
Of God and His Creatures: 2.83