When it is admitted that simple sensations remind us of one another by direct resemblance, many of the complex cases of suggestion by resemblance may be analysed into this elementary case of association by resemblance, combined with an association by contiguity. A flower, for instance, may remind us of a former flower resembling it, because the present flower exhibits to us certain qualities, that is, excites in us certain sensations, resembling and recalling to our remembrance those we had from the former flower, and these recall the entire image of the flower by the law of association by contiguity. But this explanation, though it serves for many cases of complex phenomena suggesting one another by resemblance, does not suffice for all. For, the resemblance of complex facts often consists, not solely, or principally, in likeness between the simple sensations, but far more in likeness of the manner of their combination, and it is often by this, rather than by the single features, that they recall one another. After we had seen, and well observed, a single triangle, when we afterwards saw a second there can be little doubt that it would at once remind us of the first by mere resemblance. But the suggestion would not depend on the sides or on the angles, any or all of them; for we might have seen such sides and such angles uncombined, or combined into some other figure. The resemblance by which one triangle recalls the idea of another is not resemblance in the parts, but principally and emphatically in the manner in which the parts are put together. I am unable to see any mode in which this case of suggestion can be accounted for by contiguity; any mode, at least, which would fit all cases of the kind.—Ed.
112 Mr. Hume makes contrast a principle of association, but not a separate one, as he thinks it is compounded 113 of Resemblance and Causation. It is not necessary for us to show that this is an unsatisfactory account 114 of contrast. It is only necessary to observe, that, as a case of association, it is not distinct from those which we have above explained.
A dwarf suggests the idea of a giant. How? We call a dwarf a dwarf, because he departs from a certain standard. We call a giant a giant, because he departs from the same standard. This is a case, therefore, of resemblance, that is, of frequency.
Pain is said to make us think of pleasure; and this is considered a case of association by contrast. There is no doubt that pain makes us think of relief from it; because they have been conjoined, and the great vividness of the sensations makes the association strong. Relief from pain is a species of pleasure; and one pleasure leads to think of another, from the resemblance. This is a compound case, therefore, of vividness and frequency. All other cases of contrast, I believe, may be expounded in a similar manner.
I have not thought it necessary to be tedious in expounding the observations which I have thus stated; for whether the reader supposes that resemblance is, or is not, an original principle of association, will not affect our future investigations.
12. Not only do simple ideas, by strong association, run together, and form complex ideas: but a 115 complex idea, when the simple ideas which compose it have become so consolidated that it always appears as one, is capable of entering into combinations with other ideas, both simple and complex. Thus two complex ideas may be united together, by a strong association, and coalesce into one, in the same manner as two or more simple ideas coalesce into one. This union of two complex ideas into one, Dr. Hartley has called a duplex idea.[37] Two also of these duplex, or doubly compounded ideas, may unite into one; and these again into other compounds, without end. It is hardly necessary to mention, that as two complex ideas unite to form a duplex one, not only two, but more than two may so unite; and what he calls a duplex idea may be compounded of two, three, four, or any number of complex ideas.
[37] I have been unable to trace in Hartley the expression here ascribed to him. In every passage that I can discover, the name he gives to a combination of two or more complex ideas is that of a decomplex idea.—Ed.
Some of the most familiar objects with which we are acquainted furnish instances of these unions of complex and duplex ideas.
Brick is one complex idea, mortar is another complex idea; these ideas, with ideas of position and quantity, compose my idea of a wall. My idea of a plank is a complex idea, my idea of a rafter is a complex idea, my idea of a nail is a complex idea. These, united with the same ideas of position and quantity, compose my duplex idea of a floor. In the same manner my complex idea of glass, and wood, and others, compose my duplex idea of a window; and 116 these duplex ideas, united together, compose my idea of a house, which is made up of various duplex ideas. How many complex, or duplex ideas, are all united in the idea of furniture? How many more in the idea of merchandize? How many more in the idea called Every Thing?[38] [39]
[38] This chapter raises questions of the most fundamental kind relating to our intellectual constitution. The Association of Ideas, comprehensively viewed, involves everything connected with the mental persistence and reproduction of ideas; being offered as adequate to explain the operations named Memory, Reason, and Imagination.