ABSTRACT

The Third way is drawn from the possible and the necessary, and runs as follows. Some things we encounter have the possibility of being and of not being, since we find them being generated and corrupted, and accordingly with the possibility of being and not being. Now it is impossible for all that there is to be like that; because what has the possibility of not being, at some time is not. If therefore everything has the possibility of not being, at one time there was nothing. But if this were the case, there would be nothing even now, because what is not does not begin to be except through something which is; so if nothing was in being, it was impossible for anything to begin to be, and so there would still be nothing, which is obviously false. Not everything therefore has the possibility [of being and not being], but there must be something which is necessary. Noweverything which is necessary either has the cause of its necessity outside itself, or it does not. Now it is not possible to go on for ever in a series of necessary beings which have a cause of their necessity, just as was shown in the case of efficient causes. So it is necessary to assume something which is necessary of itself, and has no cause of its necessity outside itself, but is rather the cause of necessity in other things, and this all men call God.1