On the whole, it seems to me that Aristotle's refutation of the Megarics is unsuccessful. A given assemblage of conditions is requisite for the production of any act: while there are other circumstances, which, if present at the same time, would defeat its production. We often find it convenient to describe a state of things in which some of the antecedent conditions are present without the rest: in which therefore the act is not produced, yet would be produced, if the remaining circumstances were present, and if the opposing circumstances were absent.[58] The state of things thus described is the _potential_ as distinguished from the _actual_: power, distinguished from act or energy: it represents an incomplete assemblage of the antecedent positive conditions--or perhaps a complete assemblage, but counteracted by some opposing circumstances. As soon as the assemblage becomes complete, and the opposing circumstances removed, the potential passes into the actual. The architect, when he is not building, possesses, not indeed the full or plenary power to build, but an important fraction of that power, which will become plenary when the other fractions supervene, but will then at the same time become operative, so as to produce the actual building.[59] [Footnote 58: Hobbes, in his Computation or Logic (chaps. ix. and x. Of Cause and Effect. Of Power and Act) expounds this subject with his usual perspicuity. "A Cause simply, or an Entire Cause, is the aggregate of all the accidents, both of the agents, how many soever they be, and of the patient, put together; which, when they are all supposed to be present, it cannot be understood but that the effect is produced at the same instant: and if any one of them be wanting, it cannot be understood but that the effect is not produced" (ix. 3). "Correspondent to Cause and Effect are Power and Act: nay, those and these are the same things, though for divers considerations they have divers names. For whensoever any agent has all those accidents which are necessarily requisite for the production of some effect in the patient, then we say that agent has power to produce that effect if it be applied to a patient. In like manner, whensoever any patient has all those accidents which it is requisite it should have for the production of some effect in it, we say it is in the power of that patient to produce that effect if it be applied to a fitting agent. Power, active and passive, are parts only of plenary and entire power: nor, except they be joined, can any effect proceed from them. And therefore these powers are but conditional: namely, the agent has power if it be applied to a patient, and the patient has power if it be applied to an agent. _Otherwise neither of them have power, nor can the accidents which are in them severally be properly called powers_: nor any action be said to be possible for the power of the agent alone or the patient alone."]