1 What is an oath?

• (1) The swearer makes a declaration. This may be a statement about the present or past, in which case the oath is assertory; or it may be an undertaking for the future, in which case the oath is promissory.
• (2) The swearer specifies, explicitly or implicitly,³ a superhuman power or powers ⁴ as witnesses to the declaration and guarantors of its truth. In English the swearer is said to swear “by” (sometimes, colloquially, “to”) this power or powers; in Greek the guarantor power was normally the direct object of the verb of swearing – strictly speaking, one did not in Greek “swear by Zeus”, for example; rather, one “swore Zeus”.⁵
• (3) The swearer calls down a conditional curse on him/herself,⁶ to take effect if the assertion is false or if the promise is violated, as the case may be; that is, (s)he prays that in that event (s)he may suffer punishment from the guarantor power. This element need not be explicitly spelt out; it is often left to be understood from the words of the oath itself, particularly the performative verb “I swear” (in Greek omnumi, later omnuō); but it can always be made explicit when there is need for special assurance. At any rate, whether explicit or not, it is the key defining feature of an oath: an oath is a declaration whose credibility is fortified by a conditional self-curse.⁷

• (1) In most English-speaking countries, the giving of false evidence in court trials can be prosecuted as the crime of “perjury” even if the witness has bound him/herself by solemn affirmation rather than by oath. This has created a standing temptation to use the same term as a translation of Greek pseudo-marturion “false testimony”, and even sometimes to take it for granted that witnesses in ancient Greek trials were regularly required to swear to the truth of their evidence, when in fact, at least at Athens, they were sworn only in homicide trials (and others held before the Council of the Areopagus) and in certain exceptional circumstances. For a full discussion see S&B 87-91.
• (2) The mere fact that a statement is made when the speaker is in contact with a sacred object (such as the entrails of a sacrificial animal) does not in itself make the statement into an oath, if no divine witness is explicitly or implicitly invoked. When Demaratus of Sparta puts into his mother’s hands the entrails from a sacrifice he had made to Zeus, and solemnly beseeches her to tell him truthfully who his father was (Hdt. 6.67-9; see ch. 6, p. 140 n. 31), she clearly regards herself as being under a specially binding duty to speak the truth, but nothing in her 267-word speech gives any hint that she is under oath. The episode is merely a more formal and elaborate version of the common formula whereby a question is asked, or a request made, in the name of a god (Attic Greek normally uses the preposition pros with genitive, literally “from”, e.g. pros Dios “in the name of Zeus”); this formula certainly makes a question more difficult to ignore or answer falsely, or a request more difficult to disregard, but it cannot of itself subject the addressee to a conditional curse unless the addressee him/herself invokes one. However, laying one’s hand on the earth can constitute an oath (Bacch. 5.41-2, 8.19; cf. Iliad 14.270-6), since Earth was herself a goddess; see §5.1, p. 85, and §6.3, p. 143.
• (3) In Sophocles, and very occasionally in other texts, a statement or promise which, when actually made, did not have the form of an oath, is sometimes referred to retrospectively as if it had been an oath; this phenomenon, which we call the “Sophoclean oath”, is fully discussed in §5.2. It only occurs in a small number of passages (less than one per play, even in Sophocles), and it will be shown in §5.2 that on each occasion it serves an identifiable thematic function. This does not, therefore, authorize us to treat, for example, any solemn injunction as the exacting of an oath.¹⁰