The Complete Aristotle (eng.)

another; viz. is health one? and generally
are the states and affections in bodies severally one in essence
although (as is clear) the things that contain them are obviously
in motion and in flux? Thus if a person’s health at daybreak and at
the present moment is one and the same, why should not this health
be numerically one with that which he recovers after an interval?
The same argument applies in each case. There is, however, we may
answer, this difference: that if the states are two then it follows
simply from this fact that the activities must also in point of
number be two (for only that which is numerically one can give rise
to an activity that is numerically one), but if the state is one,
this is not in itself enough to make us regard the activity also as
one: for when a man ceases walking, the walking no longer is, but
it will again be if he begins to walk again. But, be this as it
may, if in the above instance the health is one and the same, then
it must be possible for that which is one and the same to come to
be and to cease to be many times. However, these difficulties lie
outside our present inquiry.
    Since every motion is continuous, a motion that is one in an
unqualified sense must (since every motion is divisible) be
continuous, and a continuous motion must be one. There will not be
continuity between any motion and any other indiscriminately any
more than there is between any two things chosen at random in any
other sphere: there can be continuity only when the extremities of
the two things are one. Now some things have no extremities at all:
and the extremities of others differ specifically although we give
them the same name of ‘end’: how should e.g. the ‘end’ of a line
and the ‘end’ of walking touch or come to be one? Motions that are
not the same either specifically or generically may, it is true, be
consecutive (e.g. a man may run and then at once fall ill of a
fever), and again, in the torch-race we have consecutive but not
continuous locomotion: for according to our definition there can be
continuity only when the ends of the two things are one. Hence
motions may be consecutive or successive in virtue of the time
being continuous, but there can be continuity only in virtue of the
motions themselves being continuous, that is when the end of each
is one with the end of the other. Motion, therefore, that is in an
unqualified sense continuous and one must be specifically the same,
of one thing, and in one time. Unity is required in respect of time
in order that there may be no interval of immobility, for where
there is intermission of motion there must be rest, and a motion
that includes intervals of rest will be not one but many, so that a
motion that is interrupted by stationariness is not one or
continuous, and it is so interrupted if there is an interval of
time. And though of a motion that is not specifically one (even if
the time is unintermittent) the time is one, the motion is
specifically different, and so cannot really be one, for motion
that is one must be specifically one, though motion that is
specifically one is not necessarily one in an unqualified sense. We
have now explained what we mean when we call a motion one without
qualification.
    Further, a motion is also said to be one generically,
specifically, or essentially when it is complete, just as in other
cases completeness and wholeness are characteristics of what is
one: and sometimes a motion even if incomplete is said to be one,
provided only that it is continuous.
    And besides the cases already mentioned there is another in
which a motion is said to be one, viz. when it is regular: for in a
sense a motion that is irregular is not regarded as one, that title
belonging rather to that which is regular, as a straight line is
regular, the irregular being as such divisible. But the difference
would seem to be one of degree. In every kind of motion we may have
regularity or irregularity: thus there may be regular alteration,
and locomotion in a regular path, e.g. in a circle or on a straight
line, and it is the same with regard to increase and decrease. The
difference that makes a motion irregular is sometimes to be found
in its path: thus a motion cannot be regular if its path is an
irregular magnitude, e.g. a broken line, a spiral, or any other
magnitude that is not such that any part of it taken at random fits
on to any other that may be chosen. Sometimes it is found neither
in the place nor in the time nor in the