Summary: A Treatise of Human Nature (page 3)

We now come to a fundamental chapter, devoted to the connection or association of ideas. As we shall see, Hume would draw far-reaching conclusions from this.

Indeed, ideas do not remain entirely loose and unconnected ¹ since some of our ideas are complex.

Nor do they come together at random—if they did, we would never have the same complex ideas. They must therefore be connected according to universal principles, which render it, in some measure, uniform with itself in all times and places ².

However, we must bear in mind that the imagination can associate two ideas that are not naturally related, which puts the importance of these universal principles into perspective:

Without [these principles] the mind [can] join two ideas [...] we are only to regard [them] as a gentle force, which ordinarily prevails [...] nature in a manner pointing out to every one those simple ideas, which are most proper to be united into a complex one ³.

The three universal principles governing our associations of ideas are as follows:

- Resemblance: Our imagination runs easily from one idea to any other that resembles it ⁴
- Contiguity in time or space
- The cause-effect relationship.

And here is the general mechanism: Upon the appearance of one idea [they] naturally introduce another ⁵.

For example, resemblance: the idea of this pen gives rise in my mind to the idea of another pen.

Contiguity: if I am accustomed to seeing this pen next to a sheet of paper, then thinking of the pen will also bring to mind the sheet of paper.

Cause and effect: fire causes smoke; if I think of fire, the idea of smoke will also arise through association of ideas.

Hume observes that there is no relation, which produces a stronger connexion [...], and makes one idea more readily recal another, than the relation of cause and effect ⁶. He postpones its detailed examination until later.

To summarise: Two objects are connected together in the imagination [...] when the one is immediately resembling, contiguous to, or the cause of the other ⁷.

Newton had, half a century earlier, discovered the law of universal gravitation. Hume was the first to place the principle of the association of ideas at the centre of the general workings of the mind. This too is a kind of attraction, and not without pride, he casts himself as Newton's heir:

Here is a kind of ATTRACTION, which in the mental world will be found to have as extraordinary effects as in the natural, and to show itself in as many and as various forms ⁸.

Without this process of connection, we would have no complex ideas at all. This is the most remarkable effect of the association of ideas.

There are three types: relations, modes, and substances.

Relations: we acquire an idea of it by the comparing of objects ⁹.

Seven types of relations can be identified: similarity, identity, space and time, quantity, degree, contrariety, and causality.

In other words: A resembles B, A is B, A is above B, and so on.

Without resemblance, no other relation between two things can be established, for two things are compared only if they share some degree of resemblance.

Difference is the negation of a relation.

Modes and substances:

Following Berkeley, Hume criticises the notion of substance. Forty years after his illustrious predecessor, he asks: do we have a clear idea of what a substance is?

His critique rests on the epistemological framework he has just outlined.

The notion of substance comes neither from an impression of sensation nor from an impression of reflection, since it is neither an emotion nor a passion.

In fact, a substance is nothing other than a collection of particular qualities ¹⁰. As a result, the idea of a substance [...] is nothing but a collection of simple ideas, that are united by the imagination, and have a particular name assign'd them, by which we are are able to recall, either to ourselves or others, that collection ¹¹.

Here is the crux of the matter: The particular qualities, which form a substance, are commonly referr'd to an unknown something, in which they are suppos'd to inhere ¹². Thus, this colour, this degree of fusion, this solidity, are taken to be qualities of a substance: gold.

In the case of modes, by contrast, qualities are not considered as united in a single object but, on the contrary, dispers'd in different subjects ¹³. For example, the idea of dance.

Hume weighs in on the debate surrounding the status of abstract or general ideas—a debate central to scholasticism, which set nominalists against realists.

On this occasion he pays explicit tribute to Berkeley, adopting his celebrated theory that all general ideas are nothing but particular ones, annex'd to a certain term, which gives them a more extensive signification, and makes them recal upon occasion other individuals, which are similar to them ¹⁴.

For him, it is one of the greatest and most valuable discoveries that has been made of late years in the Republic of Letters ¹⁵.

The aim is to escape a false dilemma, which runs as follows: either the idea of Man represents all men of all sizes and qualities, or it represents a man without size and without quality.

The first proposition is absurd, for it would require an infinite understanding to conceive all possible sizes and qualities.

The second is equally absurd, since it is impossible to imagine a quantity or quality without its degree—one cannot imagine a line without a length. Moreover, an idea derives from an impression. Since all impressions are determined in both quality and quantity, ideas must be likewise.

Hume therefore concludes: Abstract ideas are therefore, in themselves individual, however they may become general in their representation. The image in the mind is only that of a particular object, tho' the application of it in our reasoning be the same, as if it were universal ¹⁶.

Here again, it is the mechanism of the association of ideas that does the work: certain particular ideas are habitually associated with other particular ideas, and when one is evoked, the others follow by association, through force of habit. This is how a single idea comes to represent others.

Hume sums this up as follows:

Some ideas are particular in their nature, but general in their representation. A particular idea becomes general by being annex'd to a general term; that is, to a term, which from a customary conjunction has a relation to many other particular ideas, and readily recals them in the imagination ¹⁷.

Hume's theory of knowledge thus enables him—at least in his own eyes—to resolve a centuries-old scholastic debate. All we need do is examine precisely what happens in our minds when we use a general idea, in order to determine what it actually is.

¹ 1.1.4, p.12
² Ibid.
³ P.12-13
⁴ P.13
⁵ Ibid.
⁶ Ibid.
⁷ Ibid.
⁸ P.14
⁹ 1.1.5, ibid.
¹⁰ 1.1.6, p.16
¹¹ Ibid.
¹² Ibid.
¹³ Ibid.
¹⁴ 1.1.7, p.17
¹⁵ Ibid.
¹⁶ P.18
¹⁷ P.20