Austin says that an illocutionary act may "be said to be conventional, in the sense that at least it could be made explicit by the performative formula."(1) A performative formula is a sentence whose verb is in the first person, present tense, indicative mood and names the illocutionary act performed by means of the sentence. For example, I use a performative formula when I start my argument with saying "I argue that" and so on.

(1) How to do things with Words, 2nd edition, edited by J. O. Urmson and Marina Sbisà, Oxford University Press, 1975, p. 103.

Hume may seem to think much the same way as Austin, when he says, in the third Book of the Treatise, that a certain "form of words constitutes what we call a promise," and that when "a man says he promises any thing, he in effect expresses a resolution of performing it; and along with that, by making use of this form of words, subjects himself to the penalty of never being trusted again in case of failure." (T 522(1) )

(1) References to the Treatise of Human Nature will hereafter be indicated by page numbers of the Selby-Bigge / Nidditch edition (Oxford University Press, 1978) following 'T'.

There is a seemingly obvious way of thinking, again derived from the mid-20th century philosophy of language, that would explain the importance of the conventional formula in promising. The idea is that promising is a rule-governed practice and the rules governing the practice defines the conventional formula as something that makes a promise what it is. Hume's text suggests two forms of argument along this line.

First, we might regard a promise as comparable to a move in a game. Hume compares promises to religious ceremonies like transubstantiation and holy orders. (T 524) Such ceremonies are supposed to bring changes in the nature of things and persons, but the presumed changes have no significance outside the religious practice of which such ceremonies are parts. Thus, we may say that the supposed changes are the results of moves in a game and they are unintelligible independently from the rules of the game. In such a game, the use of a certain form of words constitutes a supposed change by virtue of the rules.

Why does Hume compare promises to such moves in a game? Because, according to him, the obligation of promises does not arise from any natural act of the mind, or natural motive. Thus, the conventional formula of a promise represents nothing that is naturally intelligible. If it can constitute a promise, then it must be by virtue of a set of rules that give it its significance as a move in the game.

Second, one might argue that the rules of language give the conventional formula a privilege over other forms of words. In discussing the circumstances in which the utterance of words fails to constitute a promise, Hume mentions the knowledge of the meaning of words and the showing of a serious intention to bind oneself as necessary conditions for a promise. (T 523f.) Though Hume's discussion is too brief and unsystematic to extract from it a set of necessary and sufficient conditions for promising, the rough picture seems much the same as John Searle's analysis of illocutionary acts.(1) Among the various conditions of successful illocutionary acts that Searle proposes are: the condition that situations are appropriate, that the subject matter is suitable for being the content of a certain type of illocutionary act, for example, a promise, that parties involved are capable of normal linguistic communication, and that they have appropriate intentions. His key idea is, though, that there is a certain form of words whose use constitutes an illocutionary act of a particular kind by virtue of its meaning. Thus, when a speaker utters a certain form of words under appropriate conditions, she thereby makes a promise. Here, it is the rules of language or in Searle's terms, semantic rules, that give the conventional formula its unique function.

(1) Speech Acts, Cambridge University Press, 1969, ch. 3. In this book Searle regarded the performative formula as the typical device to perform directly the illocutionary act named by its main verb (See op. cit., pp. 30f.), but later he came to consider its use rather as an indirect speech act. See Searle and Daniel Vanderveken, Foundations of Illocutionary Logic, Cambridge University Press, 1985, pp. 2f.

As to the first suggestion, the analogy between a promise and a move in a game is only partial. The promise is a human invention, but it is invented for the sake of interest and interest is its natural obligation, while many games have nothing to do with advantage in real life. Thus, promises are not mere moves in a game but they have significance independent of any rule of the game.

The second suggestion has two obvious defects. First, one can doubt that making a promise is part of the meaning of the conventional formula. Second, even if it is part of the meaning of the conventional formula to make a promise, other forms of words seem as capable of serving to make a promise as the conventional formula.

To begin with the second point, I can make a promise by means of an ordinary indicative sentence, as explicitly as by the conventional formula. If I say to someone, "I will give you ten bucks," that would as well constitute a promise just as if I say instead, "I promise that I will give you ten bucks." These two expressions may have very different emphatic effects, but I do not think they differ in explicitness. What makes my utterance of the former sentence a promise, rather than a threat, or a simple statement of a fact, is that my giving ten bucks to the hearer is in the future, that it is within my power to do so, that it is to her advantage and so on. In short, it is the fulfillment of Searle's conditions about the situation and the subject matter. It is not the semantic rules that specify the kind of illocutionary act. Granted, my utterance of the former sentence can fail to constitute a promise, for example, if I have already promised her to give the money and then confirm by the present utterance my obligation that already exists. In that case, though, I am no more capable of making a new promise by the utterance of the latter sentence. This fact also supports the first point, that it is not part of the meaning of the conventional formula to make a promise what it is, since when a promise is not possible by other forms of words, there is no special semantic property in the conventional formula that makes it possible.

I have mentioned above a passage that at first sight seems to suggest a line of argument similar to that of Searle. I shall now examine it a bit more closely.

Hume says that after the verbal expression of promises is introduced, it "soon becomes the principal part of the promise; nor will a man be less bound by his word, though he secretly give a different direction to his intention, and withhold himself both from a resolution, and from willing an obligation." (T 523) This may be naturally understood as saying that the utterance of words with certain meaning is a sufficient condition of a promise.

This claim, though, is qualified soon after. An intention of the speaker must also attend the words. "[One] who should make use of any expression of which he knows not the meaning, and which he uses without any intention of binding himself, would not certainly be bound by it. Nay, tho' he knows its meaning, yet if he uses it in jest only, and with such signs as shew evidently he has no serious intention of binding himself, he would not lie under any obligation of performance; but 'tis necessary that the words be a perfect expression of the will, without any contrary signs." (T 523f.) This is further qualified by mentioning the case of a deceitful promise being detected. It binds the speaker though she lacks the will and the hearer knows that. (T 524)

We can understand these qualifications as Hume's attempt to capture the relation between meaning and intention in communication. Words have certain semantic properties, but we can use them to mean something only when we utter them with a set of appropriate intentions.(1) In the case of a promise, the verbal expression has the semantic properties that enable us to express the will or the intention of binding ourselves by means of it. In order to realize this capacity, though, we must have a second intention distinct from the first intention of binding ourselves. The second intention is the intention of expressing the first intention as part of the meaning of what we say. I call it the intention to communicate. There must be both of these two intentions in order to make the words "a perfect expression of the will," while one can deceitfully make a promise by expressing the second intention in the absence of the first intention. Hereafter, I shall refer to the intention of binding ourselves as the intention-B, and refer to the intention to communicate as the intention-C.

(1) I have in mind the structure of intentions of the kind proposed in the works of H. P. Grice. See his Studies in the Way of Words, Harvard University Press, 1989.

There is, though, a seemingly obvious objection to the supposition of a further intention to supplement the will expressed by a promise or intention-B. Hume repeatedly remarks that the intention-B, or the will expressed by a promise, is only feigned, and it is absurd to suppose its existence. (T 517, 523) Then, to suppose the intention-C would be at least as absurd, if not more, as the original supposition of the intention-B.

To make the matter more complicated, the same objection seems to apply to Hume's own words concerning the expression of promises. He speaks about a perfect expression of the will, but how can we give a perfect expression to a feigned, namely non-existing act of the mind?

I think the key to the solution of this difficulty lies in the distinction between the two layers in Hume's account of the obligation of promises. Hume says that it is interest that constitutes the first obligation of promises. It is sometimes called the natural obligation.(1) Then, the moral sentiments that accompany the promises constitute their moral obligation.

(1) Hume sometimes says that aritificial virtues, including the observance of promises, have no natural obligation (T 517n., 523, 525, 543), but he speaks more often about their natural obligation, namely interest, as opposed to thier moral obligation, namely moral sentiments (T 498, 545, 551, 552, 553, 568).

When Hume first discusses the verbal expression of promises, he makes no reference to a feigned act of the mind. Instead, he speaks of a resolution and a new motive additional to it. Hume says, "When a man says he promises any thing, he in effect expresses a resolution of performing it," and "A resolution is the natural act of the mind, which promises express: But were there no more than a resolution in the case, promises would only declare our former motives, and would not create any new motive or obligation. They are the conventions of men, which create a new motive." (T 522) In this, Hume may seem to contradict himself, who says several pages earlier, "The act of the mind, exprest by a promise, is not a resolution to perform any thing." (T 516) The apparent contradiction can be explained by the shift of emphasis. The point of the latter quotation is to deny that a resolution alone is sufficient for giving rise to the obligation of a promise, and not that it may sometimes or even normally attend a promise. As a matter of fact, it normally attends a promise and Hume admits that in the former quotation.

What, then, is the new motive that is created by human conventions? Since it must be some act of the mind, and in reality there can be no act of the mind attending a promise but the resolution, the answer is obvious. It must be the resolution. This is not as absurd as it may at first sound. In Hume's view, I do what I promise to someone not because of kindness or any natural affection for her. Such affections can accompany a promise, but they are not relevant to its obligation. When I resolve to do something and express the resolution in a promise, the resolution is made because of interest I have in keeping the promise. Thus, the resolution is pointless, when considered apart from the practice of promise making. In order for the obligation to attend the resolution, then, what is necessary is that the resolution is made in view of the promise and there need be no new act of the mind distinct from the resolution.

In this case, it is the resolution that fills the place of the act of the mind that gives rise to the obligation. Namely, the resolution fulfills the function attributed to the intention-B. They are, in reality, one and the same act of the mind. Since the intention-B is in reality the same with the resolution, and is a natural act of the mind when considered in itself, there is no absurdity in supposing a new intention, namely the intention-C, that derives from it.

The identity of the resolution and the intention-B also explains why the intention-B is described as feigned and totally unintelligible in connection with the moral obligation. Since the intention-B is in reality nothing but the resolution made in view of interest, it is unintelligible when considered apart from interest. When we consider the moral obligation as the sole motive of keeping promises and neglect the interest that is the first obligation of promises, we make the moral obligation unintelligible. To surmount this difficulty, we suppose the intention-B as the foundation of the moral obligation. When we think of the intention-B as a new and distinct act of the mind, though, it is totally unintelligible and must be feigned.

So far, I have considered the practice of promise-keeping as founded on interest and necessarily derived from human nature. Hume's treatment of the moral obligation, though, suggests that the practice and its obligation can extend beyond the original foundation and become, in a manner, something based on a fiction. The above-mentioned analogy with religious rites can be understood in this connection.

When we consider the practice of promising in connection with such game-like, rule-governed practices, Hume's insistence on the role of the conventional formula becomes easier to understand. Since the intentions that are supposed to be expressed by conventional formulae have no naturally intelligible content, what significance they have depends on the roles that are given to the formulae in rule-governed systems. Though, as I have argued, promises are intelligible without the conventional formula, we can understand the advantage we acquire from the introduction of the formula. It makes the obligation of promises less dependent upon particular situations by making it appear as independent from particular interest. After it is introduced, the conventional device of promises works in the same manner as conventional devices in the practice based on a fiction, regardless of the first origin of promises.

Here it is important to mark again the difference between verbal expressions in general and particular conventional formulae. Generally speaking, when a verbal expression is used to do something, the same thing can also be done by another equivalent expression. When a conventional formula is required, though, we can not do the same thing by any other means. Thus, I can promise to give a watch to someone, by saying "This watch will be yours" instead of "I will give you this watch," while in the appropriate situation you can bring in a verdict by saying "guilty"(1) but not by saying "criminal," "responsible," and so on. This shows that when conventional formulae are required, the point of their use is not only their communicative contents but also their forms. When conventional formulae do their proper work, they have to do more than merely express something by virtue of their communicative functions.

(1) The example is from P. F. Strawson, 'Intention and Convention in Speech Acts,' 1964, repr. in Searle (ed.), The Philosophy of Language, Oxford University Press, 1971, p. 26.

I summarize now my answer to the question that I have begun with. How conventional is a promise in Hume's view? As I have said before, it is conventional in the non-problematic sense that their obligation derives from agreement. As to the other sense of "conventional," in which games and ceremonies are conventional, a promise can be and in fact often is made by a conventional device. Such a device, though, is dispensable at least in principle. One reason why it is important to say this is that we tend to suppose too much when we say, as something taken for granted, that language is conventional. Language is often compared to a game, or even considered as a game, pure and simple, but I doubt the analogy is very revelatory. From the fact that illocutionary acts depend on communication and meaning it does not follow that they are moves that are intelligible only in reference to rules of the game. Hume's account of promises, in spite of its superficial appearance, does not depend on the analogy, either.