Shit has been with us an awfully long time—it appears in Old English as scitan—yet we can’t seem to agree on the past tense of the verb. Is it shit? Shat? Shitted?
My theory for why we haven’t settled this issue has partly to do with its ‑it ending, which, based on similar verbs in English, can get pulled in several different directions as we try to derive a past form. And because shit is vulgar, we generally use it less often than other verbs ending in ‑it.
So rather than having a past tense at the ready, maybe we build it on the go, by analogy:
shit (present) – shitted (simple past) – shitted (past participle)
If I coined the verb to plit and asked any native English speaker, even a young child, to tell me the past tense, they’d probably effortlessly guess it was plitted. Using the analogy to regular verbs like permit (permit – permitted – permitted) and adding ‑ed is completely intuitive and is the most common way to inflect our verbs.
We have a couple of verbs ending in ‑it—fit, knit (any more?)—that can take or leave the ‑ed inflection, though, which brings us to…
shit – shit – shit
When I searched the corpus of global web-based English (GloWbE), I found some evidence that fitted and knitted (at least as past participles) were more popular in the UK and Australia and New Zealand, whereas fit and knit were used more in North America. This trend may very well apply to shit, too; in fact, Merriam-Webster lists shit and shat as the simple past in U.S. English and doesn’t even suggest shitted as a possibility.
This type of inflection is analogous to hit – hit – hit and so also sounds perfectly natural. My only caution against using this paradigm is that some situations can lead to ambiguity. Does “The ferrets shit on your lawn” refer to a regular occurrence or something that just happened once?
Another ambiguity arises between the past participle and the noun: “They have shit” is an answer to both “Have they shit?” and “Do they have shit?”
shit – shat – shat
Inflecting verbs by changing the vowel—as in ring – rang – rung—is known as ablaut. The reason we wouldn’t say shit – shat – *shut in analogy is not only because we already have the verb shut and so using it as the past participle of shit would lead to considerable confusion, but mostly because the i – a – u ablaut occurs only before nasal sounds like [n] (begin – began – begun), [m] (swim – swam – swum), or [ŋ] (sing – sang – sung). Instead, the ablaut for shit takes on the form exemplified by sit – sat – sat.
What to use?
Because searching corpora just for shit would bring up the noun and the verb in all three tenses, I couldn’t really directly compare the frequency of the three paradigms. But a comparison of shitted and shat on Google Ngrams shows the latter coming up with about four times the frequency of the former:
and a search of the GloWbE corpus gives a ratio closer to seven. As a past participle, shat (in have/has shat) occurs a little less than twice as frequently as shit (in have/has shit), which is, in turn, quite a bit more popular than shitted (in have/has shitted).
Based on the frequency of usage, the shit – shat – shat paradigm seems to come out ahead, but any of the three is fine as long as you make sure to avoid ambiguity. Just don’t mix them: most English speakers would probably find shit – shat – shitted confusing or ungrammatical. (Fellow editors might want to start listing their preferred shit paradigm on their style sheets…)
A few extra nuggets
If you’re not a fan of uncertainty, you can always default to the noun and say take – took – taken a shit, but this cowardly move cuts out fun of sentences like “He was eminently honest and shat me not” and compounds of the verbal shit (e.g., “She admirably bullshat her way through her job interview.”)
Also, as I was digging around to see if shitten was ever used as a past participle, I found Merriam-Webster’s beautiful definition of the word as an adjective:
1. obsolete : covered with excrement : stained by excrement
2. obsolete : disgusting, contemptible
I love that the “having the quality of shit” connotation is reminiscent of how we use silken or flaxen. Now my new goal in life is—through persistent, unrelenting usage—to force the dictionary to strip off that “obsolete” label. Who’s with me?