14 
INTRODUCTION. 
times it stands for all the distinctively human faculties 
taken collectively, and in antithesis to the mental faculties 
of the brute ; while at other times it is taken to mean the 
distinctively human faculties of intellect. 
Dr. Johnson defines it as 6 the power by which man 
deduces one proposition from another, and proceeds from 
premises to consequences.’ This definition presupposes 
language, and therefore ignores all cases of inference not 
thrown into the formal shape of predication. Yet even in 
man the majority of inferences drawn by the mind never 
emerge as articulate propositions ; so that although, as 
we shall have occasion fully to observe in my subsequent 
work, there is much profound philosophy in identifying 
reason with speech as they were identified in the term 
Logos, yet for purposes of careful definition so to identify 
intellect with language is clearly a mistake. 
More correctly, the word reason is used to signify the 
power of perceiving analogies or ratios, and is in this 
sense equivalent to the term ‘ ratiocination,’ or the faculty 
of deducing inferences from a perceived equivalency of 
relations. Such is the only use of the word that is 
strictly legitimate, and it is thus that I shall use it 
throughout the present treatise. This faculty, however, 
of balancing relations, drawing inferences, and so of fore- 
casting probabilities, admits of numberless degrees ; and 
as in the designation of its lower manifestations it sounds 
somewhat unusual to employ the word reason, I shall in 
these cases frequently substitute the word intelligence. 
Where we find, for instance, that an oyster profits by 
individual experience, or is able to perceive new relations 
and suitably to act upon the result of its perceptions, I 
think it sounds less unusual to speak of the oyster as dis- 
playing intelligence than as displaying reason. On this 
account I shall use the former term to signify the lower 
degrees of the ratiocinative faculty ; and thus in my usage 
it will be opposed to such terms as instinct, reflex action, 
&c., in the same manner as the term reason is so opposed. 
This is a point which, for the sake of clearness, I desire 
the reader to retain in his memory. I shall always speak 
of intelligence and intellect in antithesis to instinct, emo* 
