Is there a difference in nuance when using once, twice or thrice instead of one time, two times or three times, especially when counting occurrences?
It has happened twice before.
It has happened two times before.
Are they always interchangeable? What about other usages (e.g. when comparing magnitude)?
The blue book is twice as heavy as the red one.
The blue book is two times as heavy as the red one.
It's actually quite unusual to see two times except in a small number of specific contexts...
two times two is four (reciting multiplication tables, in which context this chart is interesting)
three tablets two times a day (medical prescriptions)
the interval between these two times (where "times" is a noun)
my salary rose two times last year (ugly, IMHO, but people do say this sometimes)
I can't think offhand of any other usages where twice wouldn't be preferred. The picture is very different with thrice, where the short form is almost archaic, and the longer form is standard.
I understand why you might be unsure. Even this site gets it wrong, to my mind.
It's a common artefact of computer programs that generate English text by composing numbers and words.
Grammatically they are interchangeable, however 'twice' is preferred and appears more elegant.
Adding to that, many are taught that 'two times' is wrong, but this is not the case as 'two times' and 'twice' can both be used.
The same rule applies to 'trice' and 'three times', but in this case 'thrice' is almost never used. 'Once' and 'one time' are also interchangeable, however, in this case, 'once' is preferred by most people shown by Ngram.
