First causal principle: "... there must be at least as much reality in the efficient and total cause as in its effect." (IP3 52a)

(Descartes argues for this principle in the sentences which follow it.)

Descartes' Causal Principle for Objective Reality: There must be at least as much formal reality in the efficient and total cause of an idea as there is objective reality in the idea. ("in order that an idea should contain some one certain objective reality rather than another, it must without doubt derive it from some cause in which there is at least as much formal reality as this idea contains of objective reality." IP3 52b)

(Again, Descartes argues for this principle in the sentences which follow it.)