Expletive infixation (meaning the process by which you get words like ‘un-fucking-believable’, ‘irre-fucking-futable’, and yes, ‘opti-fucking-mality’) is traditionally explained based on a rule which involves the prosody (i.e., the lyrical structure) of the word. But the usual theory, which was first given by John McCarthy in his “Prosodic Structure and Expletive Infixation” is rather inadequate. It’s consistent with all of the data it provides, but it fails to give an explanation of one key phenomenon: when the word ‘destroy’ is infixed as ‘de-fucking-stroy’, the ‘de-’ becomes stressed, and the vowel lengthens from ‘deh’ into ‘dee’. Since the prosodic hypothesis states that the structure, so to speak, of the root word isn’t modified by the infix, this is hard to explain, especially since the change from ‘ih’ to ‘ee’, or [ɪ] to [iː] (see here for a chart of IPA tables) isn’t necessarily produced by stress. So another alternative is desirable.

Enter optimality theory. According to optimality theory (or OT), we can come up with a certain set of rules and a ranking for them; the valid infixation (or infixations) whose first rule violation is lower-ranked than any other infixed forms. Since some words, such as laser,cannot be infixed, the statement that ‘there must be an infixed word’ must also be a rule in and of itself, which can be violated. So let’s set up a few base rules:

• IP: The pronunciation of the infix word is preserved.
• RP: The pronunciation of the root word is preserved.
• Clash: There are no two adjacent stressed syllables.

I left out the Infix rule; we’ll come back to it later. Let’s take a look at a sample word, kindergarten (using bold for stress).

What this means is that only the first form, kinder-fucking-garten has no violatins of any rules. The other two violate one rule each; the ! indicates that each violation is the ‘first’, or highest-priority one. The two light-gray cells in the bottom row indicate that, for purposes of comparing fitness, those cells are irrelevant; in optimality theory, only the first violation is relevant.

Of course, this isn’t terribly useful for figuring out the actual rankings of constraints, and rankings are relevant; moreover, there are a few rules that haven’t been introduced yet that cannot be violated: as an example, *la-fucking-ser, despite not violating any of these rules, is not considered acceptable by the majority of English speakers. So what do we do?