The difference between ‘abstract’ and ‘concrete’ contents, which is plainly the same as Stumpf’s distinction between dependent (non-independent) and independent contents, is most important for all phenomenological investigations; we must, it seems, therefore, ﬁrst of all submit it to a thorough analysis. As said in my previous Investigation, this distinction, which ﬁrst showed up in the ﬁeld of the descriptive psychology of sense-data, could be looked on as a special case of a universal distinction. It extends beyond the sphere of conscious contents and plays an extremely important role in the ﬁeld of objects as such. The systematic place for its discussion should therefore be in the pure (a priori) theory of objects as such, in which we deal with ideas pertinent to the category of object, ideas such as Whole and Part, Subject and Quality, Individual and Species, Genus and Species, Relation and Collection, Unity, Number, Series, Ordinal Number, Magnitude etc., as well as the a priori truths which relate to these. Here again we cannot allow our analytic investigation to wait on the systematic development of our subjectmatter. Difﬁcult notions employed by us in our clariﬁcatory study of knowledge, and made to work rather in the manner of a lever, cannot be left unexamined, till they spontaneously emerge in the systematic fabric of the logical realm. For we are not here engaged on a systematic exposition of logic, but on an epistemological clariﬁcation, as well as on the prolegomena to any future exposition of logic.