The interest of this distinction of universality, particularity, and singularity lies in this, that upon it is founded the doctrine of _definition,_ since it is not possible to define, that is, to think a concept, save by thinking its _singularity_ (peculiarity), nor to think this, save by determining it as _particularity_ (relation with the other distinct concepts) and _universality_ (relation with the whole). Conversely, it is not possible to think universality without determining its particularity and singularity; otherwise that universal would be empty. The distinct concepts are defined by means of the one, and the one by means of the distinct. This doctrine, thus made clear, is also in harmony with that of the nature of the concepts. [Sidenote: _Unity, distinction as circle._] But the theory of the distinct concepts and that of their unity still present something irrational and give rise to a new difficulty. Because, if it be true that the distinct concepts constitute an ideal history or series of grades, it is also true that in such a history and series there is a _first_ and _last,_ the concept _a,_ which opens the series, and, let us say, the concept _d,_ which concludes it. Commencement and end thus remain both without motive. But in order that the concept be unity in distinction and that it may be compared to an organism, it is necessary that it have no other commencement save itself, and that none of its single distinct terms be an absolute commencement. For, in fact, in the organism no member has priority over the others; but each is reciprocally first and last. Now this means that the symbol of _linear series_ is inadequate to the concept; and that its true symbol is the _circle,_ in which _a_ and _d_ function, in turn, as first and last. And indeed the distinct concepts, as eternal ideal history, are an eternal going and returning, in which _a, b, c, d_ arise from _d,_ without possibility of pause or stay, and in which each one, whether _a_ or _b_ or _c_ or _d,_ being unable to change its place, is to be designated, in turn, as first or as last. For example, in the Philosophy of Spirit it can be said with equal truth or error that the end or final goal of the spirit is to know or to act, art or philosophy; in truth, neither in particular, but only their totality is the end; or only the Spirit is the end of the Spirit. Thus is eliminated the rational difficulty, which might be urged in relation to this part. [Sidenote: _Distinction in the pseudoconcepts._] It is still better eliminated, and the whole doctrine of the pure concepts which we have been expounding is thereby illumined and thrown into clearer outline when we observe the transformation (which we will not call either inversion or perversion), to which it is submitted in the doctrine of the pseudoconcepts. It is therefore expedient to refer rapidly to this for the sake of contrast and emphasis.