Ratnakîrtti (950 A.D.) sought to prove the momentariness of all existence (_sattva_), first, by the concomitance discovered by the method of agreement in presence (_anvayavyâpti_), and then by the method of difference by proving that the production of effects could not be justified on the assumption of things being permanent and hence accepting the doctrine of momentariness as the only alternative. Existence is defined as the capacity of producing anything (_arthakriyâkâritva_). The form of the first type of argument by anvayavyâpti may be given thus: "Whatever exists is momentary, by virtue of its existence, as for example the jug; all things about the momentariness of which we are discussing are existents and are therefore momentary." It cannot be said that the jug which has been chosen as an example of an existent is not momentary; for the jug is producing certain effects at the present moment; and it cannot be held that these are all identical in the past and the future or that it is producing no effect at all in the past and future, for the first is impossible, for those which are done now could not be done again in the future; the second is impossible, for if it has any capacity to ___________________________________________________________________ [Footnote: 1: See introduction to the translation of _Kathâvatthu_ (_Points of Controversy_) by Mrs Rhys Davids.] 159 produce effects it must not cease doing so, as in that case one might as well expect that there should not be any effect even at the present moment. Whatever has the capacity of producing anything at any time must of necessity do it. So if it does produce at one moment and does not produce at another, this contradiction will prove the supposition that the things were different at the different moments. If it is held that the nature of production varies at different moments, then also the thing at those two moments must be different, for a thing could not have in it two contradictory capacities. Since the jug does not produce at the present moment the work of the past and the future moments, it cannot evidently do so, and hence is not identical with the jug in the past and in the future, for the fact that the jug has the capacity and has not the capacity as well, proves that it is not the same jug at the two moments (_s'aktâs'aktasvabhavatayâ pratik@sa@nam bheda@h_). The capacity of producing effects (_arthakriyâs'akti_), which is but the other name of existence, is universally concomitant with momentariness (_k@sa@nikatvavyâpta_).