Idealism is not possible to infer the 'I' as an object (Descartes' "cogito ergo sum") purely from "the spontaneity of thought". Kant focused on ideas drawn from British philosophers such as Locke, Berkeley and Hume but distinguished his transcendental or critical idealism from previous varieties; Kant distinguished between things as they appear to an observer and things in themselves, "that is, things considered without regard to whether and how they may be given to us". We cannot approach the "noumenon", the "thing in Itself" () without our own mental world. He added that the mind is not a blank slate, "tabula
Cogito, ergo sum and that "I" know what "thinking" is. He suggested a more appropriate phrase would be "it thinks" wherein the "it" could be an impersonal subject as in the sentence "It is raining." The Danish philosopher Søren Kierkegaard calls the phrase a tautology in his "Concluding Unscientific Postscript". He argues that the "cogito" already presupposes the existence of "I", and therefore concluding with existence is logically trivial. Kierkegaard's argument can be made clearer if one extracts the premise "I think" into the premises "'x' thinks" and "I am that 'x'", where "x" is used as a placeholder in order to disambiguate