A text to meditate on, on the representation in connection with the conscience.
Immanuel Kant describes how the thinking person can make this reflexive return with his representations.
The I-think I must be able to accompany all my representations; for otherwise I would be representing something that could not be thought at all, which amounts to saying either that the representation would be impossible, or that, at least, it would be nothing for me. The representation that can be given before any thought is called intuition. Consequently, the whole diversity of intuition has a necessary relation to the I-think in the same subject where this diversity meets. But this representation is an act of spontaneity, that is, it cannot be considered as belonging to sensibility. I call it pure apperception to distinguish it from empirical apperception, or original apperception because it is that self-consciousness which, in producing the representation I think, must be able to accompany all the others, and which is one and identical in all conscience, cannot be accompanied by any other. I still call the unity of this representation the transcendental unity of self-consciousness, to designate the possibility of the a priori knowledge that derives from it. Indeed, the various representations that are given in a certain intuition would not be altogether my representations if they did not all belong together to a self-consciousness, i.e. insofar as they are my representations (although I am not conscious of them as such), they must nevertheless necessarily conform to the condition that alone allows them to be grouped in a general self-consciousness, since otherwise they would not belong entirely to me.
Immanuel Kant, Critique of Pure Reason (1781), “Transcendental Deduction”, § 16.