A Tripartite deity, on the other hand, is composed of multiple parts or entities, and is therefore a form of tritheism.
Trinitarians and non-Trinitarians alike hold that a tripartite deity would be composed of either finite or infinite parts. If finite, then the deity would be finite. If infinite, then there would be multiple infinities -- an irrational conclusion.
Common analogies for the distinction would be a sphere (spatially triune), or a committee of three (tripartite). The first is a single entity. The second is not.