PHILOSOPHY, MENTAL. 
consequently are never associated into com- 
plex and decomplex ideas. Just as in lan- 
guages, some letters, and combinations of 
letters, occur much more frequently than 
others, and some combinations never occur 
at all. — Further, as persons who speak the 
same language have, however, a different 
use and extent of words, so, though mau- 
kind in all ages and nations agree, in gene- 
ral, in their complex and decomplex ideas, 
yet there are many particular differences in 
them, and these differences are greater or 
less, according to the difference or resem- 
blance in age, constitution, education, pro- 
fession, country, period, &c. that is, in their 
impressions and associations. 
61. When sensations and ideas, with their 
most common combinations, have been 
often presented to the mind, a train of them, 
of considerable length, may, by once occur- 
ring, produce such a tendency to recur- 
rence, that they may recur, without the 
previous cause, in nearly the same order and 
proportion as in this single occurrence. For 
since each of the particular sensations and 
ideas is familiar, little more will be wanting 
for their recurrency than a few connecting 
links ; and even these may, in some in- 
stances, be supplied by former similar in- 
stances. These considerations, when duly 
unfolded, seem to explain the chief pheno- 
mena of memory ; and it will be easily seen 
from them, that the memory of adults, and 
of proficients in any science, ought to be 
much more ready and certain than that of 
children and novices, as it is found to be in 
fact. 
62. As many words have complex ideas 
annexed to them, so sentences, which are 
collections of words, have collections of 
complex ideas, that is, have decomplex 
ideas. And it happens in most cases, that 
the. decomplex idea belonging to any sen- 
tence, is not compounded merely to the 
complex ideas belonging to the words of it ; 
but that there are also many variations, 
some oppositions, and numberless addi- 
tions. Thus propositions, in particular, ex- 
cite, as soon as heard, assent or dissent ; 
which assent or dissent consist chiefly of 
additional complex ideas not included in 
the terms of the proposition. And it would 
be of the greatest use both in the sciences 
and in common life, thoroughly to analyse 
this matter, to show in what manner, and 
by what steps, that is, by what impres- 
sions and associations our assent and dissent, 
both in scientifical and moral subjects, is 
formed. 
Respecting the Vividness of complex Ideas, 
and the intellectual Pleasures and Pains in 
general. 
63. It is reasonable to think that some 
ideas may be as vivid as any sensation ex- 
cited by the direct action of objects r.pon 
the external organs of sense. For complex 
ideas may consist of so many parts, and 
these may so alter and exalt one another, 
that the sensorial change (whatever that be), 
may be as great as can be produced by any 
single external impression. And we know 
as a matter of fact that mental pains are 
sometimes so acute as to counterbalance, 
and even altogether remove, the attention 
from the most excruciating pain, which is 
merely that of sensation. This process may 
be assisted and accelerated by the mixture 
of vivid sensations among the ideas, by the 
sensibility of the mental frame, by a pre- 
disposition to a particular class of ideas, &c. 
— It is on this principle, in connection with 
the preceding statement, that we are en- 
abled to account for the existence of intel- 
lectual or mental pleasures and pains (that 
is, those in which no particular sensible 
pleasure or pain is perceptible), which form 
a distinct and a most important class of 
feelings. The quality of sensible pleasures 
or pains, that is, of pleasurable or painful 
sensations, unite and coalesce in the same 
manner as other ideas ; and variously con- 
nected and blended together, they consti- 
tute the whole of those internal feelings 
which we call passions, affections, emo- 
tions, &c — In almost every step of our in- 
vestigations in mental philosophy, we are 
perplexed by the scantiness of language, 
and still more by the want of precision with 
which the words we have are employed. It 
is much more easy to point out faults than 
to correct them ; but it appears to us likely 
to promote the object in one department, if 
the two classes of ideas (the relicts of sen- 
sations), viz. those which are pleasureable 
or painful, and those which are indifferent, 
or, more properly, which belong to the un- 
derstanding, were denominated tlie latter 
notions, the former feelings. Popular lan- 
guage would, in a great measure, have boi ne 
us out in this appropriation ; but, at least in 
the commencement of our statements, we 
were obliged to employ feelings in a more 
general sense, viz. for every sensorial change 
attended with consciousness, because we 
have no other word in the language com- 
prehending ideas and sensations : hencefor- 
wards, however, we wish to appropriate 
