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Shiavault - a Vault of Shia Islamic Books Philosophical Instructions Lesson Fifty-Five: Motion The Concept of Motion During the previous discussions the concept of motion became clear, and a simple definition of it was obtained: gradual change.

Other definitions of motion have been given, some of which were mentioned in the course of the preceding discussions, including ‘the gradual emergence of a thing from potentiality to actuality,’ and another definition ascribed to Aristotle, that is, ‘the first perfection of a potential existent qua potential,’ which was mentioned in Lesson Forty and which means that an existent which possesses the potentiality and capacity for a perfection but lacks it at present, will advance toward it under certain conditions, and this advancing is preparatory to the achievement of the sought perfection.

And the phrase ‘ qua potential’ is added in order to exclude the specific form of the moving existent, because every potential existent has a specific form anyway, which may be considered its first perfection, but this first perfection is with respect to its actuality rather than its potentiality, and is irrelevant to motion. The perfection of motion for a body pertains to its potentiality, and its being ‘first’ pertains to its priority for attaining its end.

However, the first definition is to be preferred because it is more concise and conceptually clear, although none of them may be considered what in logical terminology is called a ‘complete definition’ ( ḥadd-e tāmm ), because a complete definition is specific to whatnesses, which possess a genus and difference, while the concept of motion is a secondary philosophical intelligible abstracted from the manner of the moving existent, and in the external world there is no substance nor accident called motion; rather motion is the being gradual of the existence of a substance or accident and its flowing through the extension of time.

Even according to Shaykh al-Ishrāq, who considered motion to be of the category of accidents, a complete definition cannot be given for it, because its category is a highest genus and does not possess genus and difference. Another point we should mention is that instantaneous changes are abstracted from two existences, or at the least from the existence and nonexistence of a single thing, while motion is abstracted from a single existent and its extension through time.