The Cogito (n.) opened up the passage from immanence to transcendence... that is, the passage from ideas contained in the thinking substance to their 'formal existence'.
The Cogito (n.) presided over the subject's birth.
The Cogito (n.) is the initial affirmation of the privileged nature of the subject's immanent sphere... it is the affirmation of its unique place in existence.
The Cogito (n.) is the specificity of the subject's connection to the rest of reality, the sui generis nature which opens up the passage from immanence to transcendence.
Cogito (n.) is, contrary to common assumption, not a question of inference. The 'sum' is not a consequence of the thinking, but vice versa... it is the ground of thinking, the fundamentum.