It was previously indicated that it is well known among philosophers that accidental whatnesses, according to induction, possess nine higher genera, and with the addition of substance, this makes ten categories. It seems that the concepts of substance and accident are secondary philosophical intelligibles which are obtained by comparing existents with each other. For example, when one compares the existence of the states of one’s soul (not their whatnesses) with the existence of the soul (not with its whatness) he sees that the occurrence of passive qualities, such as fear, hope, happiness and sadness, etc., depends on the existence of the soul, so that on the assumption of the absence of the existence of the soul, no room remains for their existence. آموزش فلسفه ، مادي و مجرد Philosophical Instructions