My next “advanced topics in law” lecture will explore what Harvard Law Professor Charles Fried (pictured below) refers to as “the promise principle.” In brief, the proposition that “promises ought to be kept” is one of the most important normative ideals or value judgements in daily life. The promise principle is so pervasive that it informs such diverse domains as business deals, politics, and personal relationships. But why?
Broadly speaking, there are three major theories of promising. Autonomy-based or “normative power” or “will” theories of promises are premised on the idea that promises are self-imposed obligations. Broadly, speaking, all these variants of the will theory of promises generally focus on the promisor’s subjective intentions when she make a promise. Although no one is required to make a promise, once you do, you are under a self-imposed obligation to keep your word. The main problem with the will theory, however, is that it is self-refuting. If the source of a promissory obligation is the promisor’s sincere intention or will to make a binding promise on herself, then the promisor’s subsequent intention to break her promise should have the effect of producing a self-release from her original promissory obligation. That is, if one can will into existence a binding promise on oneself, then one should be able to undo a promise via one’s will as well.
Since the will theory is self-refuting, some scholars have embraced an alternative “expectations” theory of promissory obligations. In brief, this theory views the making of promises as an “expectation-producing mechanism.” That is, when a person (the promisor) makes a promise, he is making a promise to another person (the promisee), and by making a promise, the promisor is creating an expectation in the promisee that he (the promisor) will not later break his promise. To break a promise, then, is to deceive the promisee. The problem with this theory, however, is that it is open to exploitation and manipulation by the promisee. (Can you see why, or do I have to spell it out for you?)
Yet another theory is the consequentialist view of promissory obligations. Generally speaking, consequentialist or pragmatic theories take a forward-looking or probabilistic view towards promises: when deciding whether to keep or break a promise, what matters are the probable consequences of one’s promise-keeping or promise-breaking behavior. In other words, the goodness or badness of a given promise (e.g. a promise to do X) depends entirely on the consequences resulting from keeping or breaking the promise to do X. Alas, it is the forward-looking nature of consequentialist theories that prove to be their ultimate undoing, for how does one go about figuring out or guessing what these probable promissory consequences will be? At the “micro” level or in the aggregate?
The common law, however, takes a different approach to the promise principle. As I shall explain in my next lecture, only a small subset of promises are legally enforceable–namely, those backed by “bargained-for consideration” …
 See Charles Fried, Contract as Promise (Harvard Univ. Press, 1981).
 See, e.g., Book 3, Part 2, §5 of David Hume, A Treatise on Human Nature (David Fate Norton & Mary J. Norton, eds.) (Oxford Univ. Press, 2000). See also Allen Habib, Promises, in Edward N. Zalta, ed., The Stanford Encyclopedia of Philosophy (2018).
 Cf. Mary Midgley, “The Game Game,” Philosophy, Vol. 49 (1974), p. 235 (“[P]romising is everywhere a kingpin of human culture.”).
 See, e.g., Stewart Macaulay, “Non-contractual Relations in Business: A Preliminary Study,” American Sociological Review, Vol. 28 (1963), p. 58 (“Businessmen often prefer to rely on ‘a man’s word’ in a brief letter, a handshake, or ‘common honesty and decency’–even when the transaction involves exposure to serious risks.”).
 See, e.g., Ed Kilgore, “2020 Candidates Begin Signing Unity Pledge, with Sanders Taking the Lead,” New York Magazine (Apr. 26, 2019). See also Gregory Krieg, GOP Candidates Back Off Pledge to Support Nominee, CNN (Mar. 30, 2016).
 See, e.g., Johanna Peetz & Lara Kammrath, “Only Because I Love You: Why People Make and Why They Break Promises in Romantic Relationships,” Journal of Personality and Social Psychology, Vol. 100 (2011).
 See, e.g., Páll S. Ardal, “And that’s a Promise,” Philosophical Quarterly, Vol. 18 (1968), p. 234.
 See, e.g., Simon Blackburn, Oxford Dictionary of Philosophy, pp. 74-75 (Oxford Univ. Press, 2d ed., 2005).
 There is also the problem of “utility monsters,” i.e. individuals who derive large amounts of utility from their bad acts. See Robert Nozick, Anarchy, State, and Utopia, p. 41 (Basic Books, 1974). That is, consequentialist theories (both micro and macro) are problematic to the extent they are unable to provide an agreed-upon or universal definition of “utility” or offer guidance on how to measure such “utility.”
 For reference, the “micro” approach is usually referred to as act utilitarianism. By contrast, the aggregate or “macro” approach is generally referred to as rule utilitarianism or indirect utilitarianism.