PHILOSOPHY, MENTAL. 
when an end is proposed, the train of thought 
is concerned about the means, which are 
often suggested, though the object itself was 
never before in the view of the mind. All 
these relations doubtless produce their ef- 
fect by minute and almost imperceptible 
samenesses in the particular object now in 
the view of the mind, and some one which 
before has been, and has been connected 
by some cause or other with the cause or 
means by which it w as produced, or to be 
produced ; but it is convenient to speak of 
them as distinct from the more obvious re- 
lations, because they imply different culture 
of the mind, and load to sudi widely different 
effects. — Now any one of these connecting 
principles may by habit be strengthened to 
such a degree as to give us a command over- 
all the different ideas in our mind which 
have tlie given relation to each other ; so 
that when any one in the class occurs to 
ns, we have almost a certainty that it will 
suggest the rest. — As this -aiipears to be an 
indisputable fact respecting the influence of 
association, we may state it in the following 
general form : — When an idea is presented 
to the mind, either by sensation or by asso- 
ciation, bearing certain relations, either in 
itself, or in its effects on tlie mind, with ano- 
ther idea already on the mind, the latter 
is recalled by the former, and becomes con- 
nected witli it : and the association thus 
produced is subject to the same laws with 
those formed, owing to tlie contiguity in tlie 
times of the reception of the ideas. 
RESPECTING THE COMPOSITION OF IHEAS. 
53. Another grand law, or mode of, ope- 
ration, of the associative power, is that Iiy 
whicli simple ideas are formed into com- 
pound, or complex ideas ; in other words, 
more generaliy, liy which simple sensorial 
changes are combined and blended toge- 
ther. — In the consideration of tliis law, we 
shall derive most of onr statements tfom 
those of Hartley, divesting them liowever 
of those peculiarities of expression, which 
depend for tiieir correctness upon the truth 
of the positions, that the medulliiry sub- 
stance of the brain is tlie seusoriiini, and 
that sensorial changes are vibrations of the 
medullary substance. In order to explain 
Ibis law of association, it is necessary to 
take a view of the modes in which simple 
ideas, or ideas of sensation, may be asso- 
ciated. 
Case 1. Let the sensation A be often a,sso- 
ciated with each of the sensations B, C, D, 
&c. ; that is, at certain times with B, at cer- 
tain other times with C, and so on; it is 
evident from what has lieen before stated 
(§. 21.) that A, when produced alone, will 
raise a, ?i, c, d, &c. (the simple iiieas of sen- 
sation corresponding- respectively witlr A, 
B, C, D, &c.) altogether, and consequently 
will associate them together. If a, b, c, d, 
&c. are distinct in all their parts, tiien, in 
the first instance they will be merely con- 
nected, so as to make a group (which may 
be represented by a -|-fe -j- c d;) but if 
they are not distinct in tiieir pans, they 
more or less run into each other, so as to 
form a complex cluster, (wliich in-ay be re- 
presented by abed.) Now the more fre- 
quently the group a-\-b c d, &c. oc- 
curs in connection, tlie more closely the 
single ideas are united ; and unless any one 
has a peculiar degree of vividness, they will 
by degrees appear to tlie mind as one idea; 
and unless the notice of the mind is particu- 
larly directed to the circumstance tliat it is 
composed of parts, it appears as much a 
single idea as originally each of -the parts 
would have done, if the attention had been 
directed to tiiein singly. Again, the more 
the cluster abed, &c. occurs in combina- 
tion tiie more completely tlie parts coalesce, 
so that by degrees they form a complex 
idea, the parts of whidi are scarcely distin- 
guishable. 
54. Cases. If tlie sensations A, B, C, D, 
&c. be associated together, according to 
various combinations of twos, or even of 
tlirees, fours, &c. then wiil A raise up 6-[- 
c -f- d, &c. ; alsp B will raise up a c -f-d, 
&c. ; and compound or complex ideas will 
be formed of those combinations, precisely 
as was before stated in tlie case of sensa- 
tions singly associated with another sens-a- 
tion. It may happen indeed in both cases, 
that A may raise a particular idea as b, pre- 
ferably to any of the rest, in consequence 
of its being more frequently associated wilii 
fc, or of the greater novelty of the impres- 
sion of the corresponding sensation, B, ren- 
dering it more vivid, or of some tendency 
of the sensoriiim to excite b', or of some 
other cause ; and in like manner that B may 
raise c or d preferably to the rest. How- 
ever, all this will at last be over-ruled by 
the recurrence of the associations, so that 
any one of the sensations will excite tlie 
ideas of tlie rest at the same instant, and 
therefore associate them together. 
55. Case. 3. Let A, B, C, D, &c. repre- 
sent successive sensations (occurring in con- 
tiguous, successive instants,) A will raise 
