Time (_kala_) in reality consists of those innumerable particles which never mix with one another, but which help the happening of the modification or accession of new qualities and the change of qualities of the atoms. Kala does not bring about the changes of qualities, in things, but just as akas'a helps interpenetration and dharma motion, so also kala helps the action of the transformation of new qualities in things. Time perceived as moments, hours, days, etc., is called _samaya_. This is the appearance of the unchangeable kala in so many forms. Kala thus not only aids the modifications of other things, but also allows its own modifications as moments, hours, etc. It is thus a dravya (substance), and the moments, hours, etc., are its paryayas. The unit of samaya is the time required by an atom to traverse a unit of space by a slow movement.