There are two main relations recognised in the Nyaya Vaisesika philosophy. These are samyoga or conjunction which is a temporary inherence.
Conjunction is a temporary or non-eternal reution between two things which can, and usually do, exist in separation from each other. Two balls moving from opposite directions meet at a certain place.
The relation which holds between them when they meet is one of conjunction. It is a temporary contact between two substances which may again be separated and yet exist (yutasiddha).
So long as the relation of conjunction is, it exists as a quality of the terms related by it. But it does not affect the existence of those terms.
It makes no difference to the existence of the balls whether they are conjoined to each other or not. Thus conjunction is an external relation which exists as an accidental quality of two substances related by it.
As distinguished from conjunction, samavaya is a permanent or eternal relation between two entities, of which one inheres in the other.
The whole is in its parts, a quality or an action is in a substance, or the universal is in the individuals, and particularity is in some simple eternal substance.
Thus we say that the cloth as a whole is in the threads, the colour red as a quality is in the rose, motion as an action belongs to the moving ball, manhood as a universal is in individual men, and the peculiarity or the distinctive character of one mind or soul is in that mind or soul. Samavaya is perceptible, according to Nyaya, but not so, according to Vaisesika.
Conjunction is a temporary relation between two things which can exist separately, and it is produced by the action of either or both of the things related, e.g.
The relation between a man and the chair on which he may be seated for the time being. On the other hand, the whole is always related to its parts, a quality or an action is always related to some substance, and so forth.
So long as any whole, say ajar, is not broken up, it must exist in the parts. So also, any quality or action must be related to some substance as long as it exists.
Thus we see that the relation of a whole to its parts, of any quality or action to its substance, of the universal to the individual, and of particularity to the eternal substances is not produced by the conjunction of to separate things.
Hence it is that they are said to be related without conjunction (ayutasiddha). Samavaya is thus an eternal relation (ayutasiddha). Samavaya is thus an eternal relation between anv two entities, one of which cannot exist without the other.
Terms related by samavaya cannot be reversed like those related by samyoga. If there is a contact of the hand with a pen, the pen also must be in contact with the hand; but though a quality is in a substance, the substance is not in the quality.