Tahafut_al-Tahafut-transl-Engl-van-den-Bergh

not, and of the possible with equal chances of happening, and these three
types of the possible do not seem to have the same need for a new
determining principle. For the possible that happens more often than not is
frequently believed to have its determining principle in itself, not outside,
as is the case with the possible which has equal chances of happening
and not happening. Further, the possible resides sometimes in the agent,
i.e. the possibility of acting, and sometimes in the patient, i.e. the
possibility of receiving, and it does not seem that the necessity for a
determining principle is the same in both cases. For it is well known that
the possible in the patient needs a new determinant from the outside; this
can be perceived by the senses in artificial things and in many natural
things too, although in regard to natural things there is a doubt, for in most
natural things the principle of their change forms part of them. Therefore it
is believed of many natural things that they move themselves, and it is by
no means self-evident that everything that is moved has a mover and that
there is nothing that moves itself.; But all this needs to be examined, and
the old philosophers have therefore done so. As concerns the possible in
the agent, however, in many cases it is believed that it can be actualized
without an external principle, for the transition in the agent from inactivity
to activity is often regarded as not being a change which requires a
principle; e.g. the transition in the geometer from non-geometrizing to
geometrizing, or in the teacher from non-teaching to teaching.
Further, those changes which are regarded as needing a principle of
change can sometimes be changes in substance, sometimes in quality, or
in quantity, or in place.
In addition, ‘eternal’ is predicated by many of the eternal-by-itself and
the eternal-through-another. According to some, it is permissible to admit
certain changes in the Eternal, for instance a new volition in the Eternal,
according to the Karramites, and the possibility of generation and
corruption which the ancients attribute to primary matter, although it is
eternal. Equally, new concepts are admitted in the possible intellect
although, according to most authors, it is eternal. But there are also
changes which are inadmissible, especially according to certain ancients,
though not according to others.
Then there is the agent who acts of his will and the agent which acts by
nature, and the manner of actualization of the possible act is not the same
34