That upon which something depends in some way for being; the reason for something. 

Intrinsic Causes.— Causes that constitute the essence of a thing. E.g., in bodies these are primary matter and substantial form. 

Extrinsic Causes.— Causes apart from a thing’s essence that determine it in some way. E.g., efficient causes, final causes, extrinsic formal causes.  The latter is sub-divided into exemplar and objective causality, with the last being likewise subdivided into vicarious (or signitive) and non-vicarious objective causality.  Sometimes, extrinsic formal causality is said to contain the species of moral causality, which can be in some way reduced to objective causality, whether vicarious or not. 

Mutual reciprocity of causes.  The principle by which two causal lines co-determine each other, as do form and matter, and also final and efficient causes.