This separation of the two phases essential to the process of art-production carries with it the result that the various forms which find their place in the entire subject-matter under discussion have merely a claim to fall in as part of an inquiry into the modes of art in virtue of the fact that poetry, and only poetry, is in a position to express such a relation of self-contained independence as between significance and form. As opposed to this it is the very problem of the plastic arts to manifest such significant content in and through their external form and viewed thus externally. A. MODES OF COMPARISON, WHICH HAVE THEIR ORIGIN UPON THE SIDE OF EXTERNALITY The attempt to arrange the several kinds of poetic production which are apportioned to this first stage of the comparative type of art carries with it no little difficulty, and is a fruitful source of embarrassment. They are, that is to say, hybrid species of a subordinate rank, which in no way whatever mark out any necessary aspect of art They stand in the domain of Aesthetic presenting features analogous to certain animal types, and other exceptional phenomena in natural science. In both spheres the difficulty consists in this that in either case it is the notion of the science itself, which is the ground of its classification and specific differences. As differentia of the notion these are also at the same time distinctions really adequate to the notional process, and intelligible as such; with these latter such transitional modes are unable fully to conform for the reason that they are merely defective types, which proceed from a previous phase that is fundamental without being able to reach the next one. This is no fault of the notion, nay, supposing that we preferred to make such ancillary types the basis of our classification, instead of pointing out their relation to the specific phases of the _notional_ process of our subject-matter, we should have presented us precisely that aspect of them which was inadequate to this process as the irreproachable mode of their development. A true principle of classification, on the contrary, is compelled to proceed from the true notion, and such _hybrid_ types as those now discussed can only be suitably placed where the genuine and independently stable ones show a tendency to dissolve and pass over into others.