Dr. Thomas Brown observes, in his inquiry into Cause and Effect--"From the mere silence of any one, we cannot infer that he is dumb in consequence of organic imperfection. He may be silent only because he has no desire of speaking, not because speech would not have followed his desire: and it is not with the mere _existence_ of any one, but _with his desire of speaking_, that we suppose utterance to be connected. A man who has _no desire of speaking, has in truth_, and in strictness of language, _no power of speaking, when in that state of mind_: since he has not a circumstance which, as immediately prior, is essential to speech. But since he has that power, as soon as the new circumstance of desire arises--and as the presence or absence of the desire cannot be perceived but in its effects--_there is no inconvenience in the common language_, which ascribes the power, _as if it were possessed at all times, and in all circumstances of mind_, though unquestionably, nothing more is meant than that the desire existing will be followed by utterance." (Brown, Essay on the Relation of Cause and Effect, p. 200.) This is the real sense of what Aristotle calls [Greek: to\ de\ (le/getai) dunato/n, oi(=on dunato\n ei)=nai badi/zein o(/ti badiseien a)\n], _i.e._ he will walk _if_ he desires to do so (De Interpret. p. 23, a. 9-15).] 4. According to the Megaric doctrine (says Aristotle) when you are now lying down, you have no power to rise: when you are standing up, you have no power to lie down: so that the present condition of affairs must continue for ever unchanged: nothing can come into existence which is not now in being.--Here again, the Megarics would have denied his inference. The man who is now standing up, has power to lie down, _if he wills_ to do so--or he may be thrown down by a superior force: that is, he will lie down, _if_ some new fact of a certain character shall supervene. The Megarics do not deny that he has power, _if_--so and so: they deny that he has power, without the _if_--that is, without the farther accompaniments essential to energy. [Side-note: Potential as distinguished from the Actual--What it is.]