PREFACE,

XX1

ance with the instruments employed, or much
thought regarding the methods of applying
them: and although his logical powers kept
him in general to the employment of a term in
one uniform sense when he clearly discerned it,
yet, in cases where he happened unconsciously
to change the meaning, or to be unaware of an
ambiguity, his inaptness at analysis precluded
all chance of his subsequently correcting any
deviation, and the very strictness of his deductions
 only led him further into error. Starting
from a given proposition, he would reason from
it with admirable closeness, but he seems never
to have been sent back, by the strangeness of the
results at which he arrived, to a reconsideration
of the principle from which he set out, nor to
have been roused to a suspicion of some lurking
 ambiguity in his terms. Hence it might
have been predicted, that he would commit
oversights in his premises and assumptions, for