  In order to produce knowledge about the world as a whole, philosophy cannot rely on empirical methods like the specialized sciences do, nor can it simplistically project one concept or set of concepts describing one of the world’s parts onto the world-whole. For Rickert philosophy has to rely on what he calls “the heterological principle” (Rickert 1921b, 57; Rickert 1934b, 39). Scholars agree that the notion of heterology is the most distinctive element of Rickert’s philosophy (Glockner 1937, 11; Flach 1958, 564; Orth 1998, 81) and even his “principle of all principles” (Krijnen 2001, 256). Heterology is a relational mode of thinking, which Rickert considers paramount to the theoretical determination of objects in general (Rickert 1921b, 57) and utterly unavoidable for a conceptual grasp of totalities. It consists in using a pair of mutually exclusive concepts, that is, concepts that negate each other, and take them together as complementary. To think heterologically means to posit a given initial concept (thesis) and then proceed to posit a second concept that can be seen as its ‘other’ (hetero-thesis), so that the two concepts taken together cover the entirety of the totality to be theoretically determined. “Wherever we can construct concepts that, through their determinations (i.e., their limitations), do not merely negate, but they simultaneously determine positively the negated component that is missing from the whole, we can think in terms of alternatives. In so doing we are able to grasp conceptually, through a kind of detour, a whole that cannot be grasped through concepts in a direct fashion. This is because we can construct two concepts, under which every element belonging to the whole necessarily falls” (Rickert 1934b, 34). We already encountered heterological pairs of concepts in the previous sections, for instance, the transcendental-psychological and the transcendental-logical paths in the theory of knowledge and generalizing and individualizing concept formation in the theory of science (see above.) In both cases the two opposite concepts, if taken together, circumscribe a totality: in the first case, the totality of epistemology, and, in the second case, the totality of scientific methods in empirical research. The ‘test’ for successful heterological reasoning is that the negation of one of the two related concepts results positively into the other concept, so that one can be a priori certain that any item not falling under the first concept necessarily falls under the second concept. As an example Rickert illustrates how to determine heterologically the totality of bodies (Rickert 1934b, 42). We can start with the thesis ‘organic living bodies’ and if we proceed to negate it we see that the merely negative concept ‘~ organic living bodies’ immediately results in the positive concept ‘dead mechanical bodies’. Taken together the two concepts amount to a successful theoretical grasp of the whole ‘bodies’. We can see with evidence that within the totality ‘bodies’, whatever body does not fall under the category ‘organic living body’ necessarily falls under the category ‘dead mechanical body’. Using heterology philosophy can reflect upon the world as a whole in terms of “world-alternatives” (Rickert 1934b, 42) and set out to determine what pair of concepts is best suited to encompass the totality of what is. As we know from previous sections, Rickert contends that the pair of concepts nature/psyche does not withstand the heterological test, in that what is not nature can be either psyche or timelessly valid value. Ultimately for Rickert the correct heterology in terms of which we can approach philosophically the world as a whole is reality/value (Rickert 1913, 11). This is because whatever is not an empirical reality (be it physical or psychic) lies necessarily in the sphere of value and vice versa. Once this broad categorization of the world as whole is established, philosophy can set out to determine more specifically the subordinated wholes out of which the world as a whole is constituted and to articulate meaningfully their mutual relations.