Spinoza's Ethics: I.P31: Intellect in Action

Spinoza distinguishes clearly here between our intellect, which is a mode of the attribute of thought, and the attribute of thought. Our intellect is just one of an array of modes of thought. The attribute of thought which he calls absolute thought is of a completely different order. He then addresses the issue of the intellect insofar as it relates to the activity of understanding. He is careful to not address the potential for thinking, because he is demonstrating how the intellect functions within a framework of modal causality.

Intellectus actu sive is finitus sit sive infinitus, ut et voluntas, cupiditas, amor etc. ad Naturam naturatam, non vero ad naturantem referri debent. 

Translated as,

The intellect, whether finite or infinite in action, like will, desire, love, etc. ought to be referred to as Nature natured, not as Nature naturing.

Demonstratio: Per intellectum enim (ut per se notum) non intelligimus absolutam cogitationem sed certum tantum modum cogitandi, qui modis ab aliis scilicet cupiditate, amore, etc. differt adeoque (per definitionem 5) per absolutam cogitationem concipi debet nempe (per propositionem 15 et definitionem 6) per aliquod Dei attributum quod aeternam et infinitam cogitationis essentiam exprimit, ita concipi debet ut sine ipso nec esse nec concipi possit ac propterea (per scholium propositionis 29) ad Naturam naturatam, non vero naturantem referri debet ut etiam reliqui modi cogitandi. Q.E.D.

Translated as,

By intellect (as is known through itself) we understand not absolute thought, but only a certain mode of thinking, which mode differs from the others, such as desire, love, etc., and to such a degree (by D5) truly ought to be conceived by absolute thought, that is (by P15 and D6), it must be conceived in this way by some attribute of God which expresses the eternal and infinite essence of thought so that without that attribute it can neither be nor be conceived and so (by P29S) like the other modes of thinking, it must be referred to as Nature natured not as Natura naturing.

Scholium: Ratio cur hic loquar de intellectu actu non est quia concedo ullum dari intellectum potentia sed quia omnem confusionem vitare cupio, nolui loqui nisi de re nobis quam clarissime percepta, de ipsa scilicet intellectione qua nihil nobis clarius percipitur. Nihil enim intelligere possumus ad perfectiorem intellectionis cogitationem non conducat.

Translated as,

The reason why I speak here of the intellect in action is not because I concede that there is an intellect in potential, but, because I wish to avoid all confusion, I do not wish to speak of things unless we perceive [them] as clearly as possible.  Certainly concerning intellectual activity itself, nothing is more clear to our perception. For we are able to understand nothing that does not lead to more perfect thinking of intellectual activity.