Spinoza's Ethics: II.P21

Here Spinoza reaches the sense that occurs in meditation or reflective thought. At times we think simply as the mind connected to the body or sensation or object. However, he outlines that the same connection can occur when the mind is connected to the mind and reflects on cognition itself. The form of the idea allows for that idea as such to become the idea of the mind, or the idea of the idea.

Hæc mentis idea eodem modo unita est menti ac ipsa mens unita est corpori.

Translated as,

This idea of the mind is united in the the same way to the mind as the mind itself is united to the body.

DEMONSTRATIO: Mentem unitam esse corpori ex eo ostendimus quod scilicet corpus mentis sit objectum (vide propositiones 12 et 13 hujus) adeoque per eandem illam rationem idea mentis cum suo objecto hoc est cum ipsa mente eodem modo unita esse debet ac ipsa mens unita est corpori. Q.E.D.

Translated as,

That the mind is united to the body from this we show because just as the body is the object of the mind (see IIP12 and 13) to such a degree by that same reasoning the idea of the mind with its own object that is since by the mind itself in the same way ought to be united as the mind itself is united to the body.

SCHOLIUM: Hæc propositio longe clarius intelligitur ex dictis in scholio propositionis 7 hujus; ibi enim ostendimus corporis ideam et corpus hoc est (per propositionem 13 hujus) mentem et corpus unum et idem esse individuum quod jam sub cogitationis jam sub extensionis attributo concipitur; quare mentis idea et ipsa mens una eademque est res quæ sub uno eodemque attributo nempe cogitationis concipitur. Mentis inquam idea et ipsa mens in Deo eadem necessitate ex eadem cogitandi potentia sequuntur dari. Nam revera idea mentis hoc est idea ideæ nihil aliud est quam forma ideæ quatenus hæc ut modus cogitandi absque relatione ad objectum consideratur; simulac enim quis aliquid scit, eo ipso scit se id scire et simul scit se scire quod scit et sic in infinitum. Sed de his postea.

Translated as,

This proposition is understood by far more clearly from statements in the IIP7S; for there we show the idea of the body and the body that is (by IIP13) the mind and the body are one and the same to be indivisible because it is conceived at one time under the attribute of thought and at another under the attribute of extension; wherefore the idea of the mind and the mind itself are the same thing is a thing which of course is conceived under the one and the same attribute of thought. I say the idea of the mind the the mind itself in God follow to exist by the same necessity from the same power of thinking. For actually the idea of the mind that is the idea of the idea is nothing other than the form of the idea insofar as this as a way of thinking and is considered away from the relationship to its object; and at the same time anyone might know anything, in this way itself knows itself that it knows it and at the same time knows that it knows because it knows and on to infinitum. But later on these things.