A cause is defined as an unconditional and invariable antecedent of an effect and an effect as an unconditional and invariable consequent of a cause. The same cause produces the same effect; and the same effect is produced by the same cause. The cause is not present in any hidden form whatsoever in its effect.
The following conditions should be met:
# The cause must be antecedent [Purvavrtti]
# Invariability [Niyatapurvavrtti]
# Unconditionality [Ananyathasiddha]
Nyaya recognizes five kinds of accidental antecedents [Anyathasiddha]
# Mere accidental antecedent. E.g., The colour of the potter's cloth.
# Remote cause is not a cause because it is not unconditional. E.g., The father of the potter.
# The co-effects of a cause are not causally related.
# Eternal substances, or eternal conditions are not unconditional antecedents, e.g. space.
# Unnecessary things, e.g. the donkey of the potter.
Nyaya recognizes three kinds of cause:
# Samavayi,  material cause, e.g. thread of a cloth.
# Asamavayi, colour of the thread which gives the colour of the cloth.
# Nimitta, efficient cause, e.g. the weaver of the cloth.