28
A single science is one whose domain is a single genus, viz. all the
subjects constituted out of the primary entities of the genus-i.e. the
parts of this total subject-and their essential properties.
One science differs from another when their basic truths have
neither a common source nor are derived those of the one science
from those the other. This is verified when we reach the
indemonstrable premisses of a science, for they must be within one
genus with its conclusions: and this again is verified if the
conclusions proved by means of them fall within one genus-i.e. are
homogeneous.
29
One can have several demonstrations of the same connexion not only
by taking from the same series of predication middles which are
other than the immediately cohering term e.g. by taking C, D, and F
severally to prove A-B--but also by taking a middle from another
series. Thus let A be change, D alteration of a property, B feeling
pleasure, and G relaxation. We can then without falsehood predicate
D of B and A of D, for he who is pleased suffers alteration of a
property, and that which alters a property changes.
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