Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
PLUPLUPERFECT TENSE
If only we would’ve known, we’d’ve stopped them contains a plupluperfect (sometimes called superpluperfect), a verb (known) with two auxiliaries, one of them redundant. Either auxiliary can be a contraction (If only we’d have known,…), and the uncontracted auxiliaries can be either would have or had have. All such locutions are Substandard, although the plupluperfect can occur in Standard jocular use (a measure of how certain the speaker is that Standard listeners will recognize the joke), which, when written, often uses of in place of the contraction ’ve; We’d of loved to see them. Spoken or written inadvertently, the plupluperfect is a powerful shibboleth in Standard English.
