in point of nature, the being of each of which involves that of the
other, while at the same time neither is the cause of the other's
being. This is the case with regard to the double and the half, for
these are reciprocally dependent, since, if there is a double, there
is also a half, and if there is a half, there is also a double,
while at the same time neither is the cause of the being of the other.
Again, those species which are distinguished one from another and
opposed one to another within the same genus are said to be
'simultaneous' in nature. I mean those species which are
distinguished each from each by one and the same method of division.
Thus the 'winged' species is simultaneous with the 'terrestrial' and
the 'water' species. These are distinguished within the same genus,
and are opposed each to each, for the genus 'animal' has the 'winged',
the 'terrestrial', and the 'water' species, and no one of these is
prior or posterior to another; on the contrary, all such things appear
to be 'simultaneous' in nature. Each of these also, the terrestrial,
the winged, and the water species, can be divided again into
subspecies. Those species, then, also will be 'simultaneous' point
of nature, which, belonging to the same genus, are distinguished
each from each by one and the same method of differentiation.
But genera are prior to species, for the sequence of their being
cannot be reversed. If there is the species 'water-animal', there will
be the genus 'animal', but granted the being of the genus 'animal', it
does not follow necessarily that there will be the species
Those things, therefore, are said to be 'simultaneous' in nature,
the being of each of which involves that of the other, while at the
same time neither is in any way the cause of the other's being;
those species, also, which are distinguished each from each and
opposed within the same genus. Those things, moreover, are
'simultaneous' in the unqualified sense of the word which come into
being at the same time.