Plato restricts the conception of Not-being to difference. Man is a rational animal, and is not--as many other things as are not included under this definition. He is and is not, and is because he is not. Besides the positive class to which he belongs, there are endless negative classes to which he may be referred. This is certainly intelligible, but useless. To refer a subject to a negative class is unmeaning, unless the 'not' is a mere modification of the positive, as in the example of 'not honourable' and 'dishonourable'; or unless the class is characterized by the absence rather than the presence of a particular quality. Nor is it easy to see how Not-being any more than Sameness or Otherness is one of the classes of Being. They are aspects rather than classes of Being. Not-being can only be included in Being, as the denial of some particular class of Being. If we attempt to pursue such airy phantoms at all, the Hegelian identity of Being and Not-being is a more apt and intelligible expression of the same mental phenomenon. For Plato has not distinguished between the Being which is prior to Not-being, and the Being which is the negation of Not-being (compare Parm.). But he is not thinking of this when he says that Being comprehends Not-being. Again, we should probably go back for the true explanation to the influence which the Eleatic philosophy exercised over him. Under 'Not-being' the Eleatic had included all the realities of the sensible world. Led by this association and by the common use of language, which has been already noticed, we cannot be much surprised that Plato should have made classes of Not-being. It is observable that he does not absolutely deny that there is an opposite of Being. He is inclined to leave the question, merely remarking that the opposition, if admissible at all, is not expressed by the term 'Not-being.'