The ‘I’ is a bare consciousness, accompanying all concepts. In the ‘I’, ‘nothing more is represented than a transcendental subject of thoughts’. ‘Consciousness in itself (is) not so much a representation…as it is a form of representation in general.’ The ‘I think’ is ‘the form of apperception, which clings to every experience and precedes it.’Kant grasps the phenomenal content of the ‘I’ correctly in the expression ‘I think’, or—if one also pays heed to including the ‘practical person’ when one speaks of ‘intelligence’—in the expression ‘I take action’. In Kant’s sense we must take saying “I” as saying “I think.” Kant tries to establish the phenomenal content of the “I” as *res cogitans*. If in doing so he calls this “I” a ‘logical subject’, that does not mean that the “I” in general is a concept obtained merely by way of logic. The “I” is rather the subject of logical behavior, of binding together. ‘I think’ means ‘I bind together’. All binding together is an ‘*I* bind together’. In any taking-together or relating, the “I” always underlies—the ὑποκείμενον [hypokeimenon; subjectum; subject]. The *subjectum* is therefore ‘consciousness in itself’, not a representation but rather the ‘form’ of representation. That is to say, the “I think” is not something represented, but the formal structure of representing as such, and this formal structure alone makes it possible for anything to have been represented. When we speak of the “form” of representation, we have in view neither a framework nor a universal concept, but that which, as εἶδος [eidos], makes every representing and everything represented be what it is. If the “I” is understood as the form of representation, this amounts to saying that it is the ‘logical subject’.Kant’s analysis has two positive aspects. For one thing, he sees the impossibility of ontically reducing the “I” to a substance; for another thing, he holds fast to the “I” as ‘I think’. Nevertheless, he takes this “I” as subject again, and he does so in a sense which is ontologically inappropriate. For the ontological concept of the subject *characterizes not the Selfhood of the “I” qua Self, but the self-sameness and steadiness of something that is always present-at-hand*. To define the “I” ontologically as “*subject*” means to regard it as something always present-at-hand. The Being of the “I” is understood as the Reality of the *res cogitans*."―from_Being and Time_. Translated by John Macquarrie & Edward Robinson, pp. 366-367
Martin Heidegger
heidegger, kant, metaphysics, ontology, philosophy, reality