“It never truly sunk in, ...”: Sunk or sank?

Question

I just began reading The Only Grammar Book You’ll Ever Need by Susan Thurman. On the first page of the Introduction chapter, the author wrote

“Maybe all that talk in English class about parts of speech and dangling participles never truly sunk in, ...”

I’ve researched the differences between sunk and sank: sunk is the past participle of sink, and sank is the past tense. However, I still cannot tell whether the usage of sunk in the aforementioned excerpt is correct. This is likely because my understanding of past participles and past tenses is not sophisticated enough.

I would greatly appreciate it if people would please take the time to clarify this and provide an explanation.

Answer 1

To some speakers, the phrasal verb sunk in sounds better than sank in. This Ngram shows that never really sank in and never really sunk in are about the same.

The Oxford Dictionary online has a usage note at sink:

Historically, the past tense of sink has been both sank and sunk (the boat sank; the boat sunk) and the past participle has been both sunk and sunken (the boat had already sunk; the boat had already sunken). In modern English the past is generally sank and the past participle is sunk, with the form sunken now surviving only as an adjective, as in a sunken garden or sunken cheeks.

Which coincides with my American English experience of almost always using or hearing only sank as the past simple. To me, sunk as the past simple seems marked or off or nonstandard or pirate or drunk pirate or drunken pirate, but your mileage may vary.

So that's probably not the only grammar book you'll ever need.

Answer 2

The New Oxford American Dictionary says the past of sink is "sank or sunk", and the past participle is sunk. So this sentence is still correct, even it is the simple past (I think it is).