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

as the differences depend on differences between the four causes, the
question is clear. For the differentiation of the spheres arises from the
differences of their movers, of their forms, of their matter, supposing they
have matter,’ and of their acts which serve a special end in the world,
even if the philosophers did not believe that these spheres exist for the
sake of these acts As to the differences which arise primarily in the
sublunary world in the elements, as for instance the differences between
fire and earth, and in short the opposites, they are based on the
differentiation of matter and on their varying distances from their movers,
which are the heavenly bodies. As to the difference between the two
supreme movements, one of which is the agent of generation and the
other the agent of corruption, they depend on the differentiation of the
heavenly bodies and their motions, as is proved in the book On
Generation and Corruption. For the difference which arises from the
heavenly bodies resembles the difference which arises from the difference
in the instruments. To sum up: the factors for the origination of plurality
from the one Agent are three, according to Aristotle, and he refers to the
One in the sense mentioned above, namely, that the One is the cause of
the plurality. In the sublunary world the differences arise from the four
causes, that is to say, the difference of the agents, the matter, the
instruments, and the intermediaries which transmit the acts of the First
Agent without its direct interference, and those intermediaries are very
similar to the instruments. And an example of the differentiation which
arises through the difference of the recipients, and out of the fact that
certain differentiated things cause others, is colour. For the colour which
arises in the air differs from the colour in the body, and the colour in the
faculty of sight, i.e. in the eye, from the colour in the air, and the colour in
the common internal sense from the colour in the eye, and the colour in
the imagination from the colour in the common internal sense, and the
colour in the memorative and retentive faculty from the colour in the
imagination; and all this has been explained in the book of psychology.
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