Full Idea
My existence cannot be regarded as inferred from the proposition "I think" (for otherwise the major premise "Everything that thinks, exists" would have to precede it), but rather it is identical with it.
Gist of Idea
'I think therefore I am' is an identity, not an inference (as there is no major premise)
Source
Immanuel Kant (Critique of Pure Reason [1781], B422)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.453
A Reaction
"I think" can hardly be identical with "I exist". One is an activity, the other a state. I prefer: within the unified activity of thinking which is clearly occurring, it is self-evident that there must be an 'I' which holds it together.