Chapter 13
Things are called simultaneous simply and most properly, whose generation occurs at the same time, for neither is prior or posterior; these, therefore, are said to be simultaneous as to time. But by nature those are simultaneous, which reciprocate according to the consequence of existence, although one, is by no means the cause of the existence of the other, as in the double and the half, for these reciprocate; thus the double existing, the half also exists, and the half existing, the double exists, but neither is the cause of existence to the other.
Those, also, which being derived from the same genus, are by division mutually opposed, are said to be naturally simultaneous; but they, are said to have a division opposite to each other, which subsist according to the same division; thus the winged is opposed to pedestrian and aquatic, as these being derived from the same genus, are by division mutually opposed, for animal is divided into these, viz. into the winged, the pedestrian, and aquatic, and none of these is prior or posterior, but things of this kind appear naturally simultaneous. Each of these again, may be divided into species, for instance, the winged, the pedestrian, and the aquatic; wherefore, those will be naturally simultaneous which, derived from the same genus, subsist according to the same division. But genera are always prior to species, since they do not reciprocate according to the consequence of existence; for the aquatic existing, animal exists, but though animal exists, it is not necessary that the aquatic should.
Hence those are called naturally simultaneous, which indeed reciprocate, according to the consequence of existence; but the one is by no means the cause of existence to the other, which is also the case with things that, derived from the same
