As is well known, even adults speaking their native language occasionally make grammatical mistakes. These can be slips of the tongue, which may then be corrected in the same breath. But they may also be out and out errors which go uncorrected for one or another reason, including lack of awareness on the utterer’s part that an error has been committed.
Errors are not uniformly of the same kind. Roughly speaking, they fall into two main categories, motivated and unmotivated. The first category subsumes those that lend themselves to some kind of reasoned explication; the second, those that are catachrestic pure and simple.
On the National Public Radio program “Morning Edition” (VPR, January 24, 2011), the host, Renee Montagne, was interviewing the economics editor of The Wall Street Journal, David Wessel, who uttered the phrase “one of the poster childs,” i. e., failed to say the grammatically correct form of the plural, children. This mistake allows for a quasi-explanation, in that there exists at least one precedent for a deviation from the normal plural, namely in the phrase still lifes (when speaking of an art object). Here a distinction is being made between the plural of life in the ordinary sense (lives) and its special transferred sense in the case of a genre of pictorial representation.
No such explication of motivatedness in the grammatically strict sense is available, however, for the blunder the same host made in the interview a few minutes later, when she uttered (without self-correction) the mangled form *magnimonious instead of the correct magnanimous. This instance of catachresis was evidently the simple product of contamination between adjectives that sound vaguely alike (sanctimonious? parsimonious?).