If something is still unknown and we want to say that it will happen only in the future that we learn about it, is it correct to say like this:
We already know some details, but the rest is still to be learnt/learned.
EDIT I am not asking what version of past participle of the verb to learn is valid - it would be another question, but instead I mean the structure still to be PP
From the Grammarist
Learned vs. learnt Learned is the more common past tense and past participle of the verb learn. Learnt is a variant especially common outside North America. In British writing, for instance, it appears about once for every three instances of learned. In the U.S. and Canada, meanwhile, learnt appears only once for approximately every 500 instances of learned, and it’s generally considered colloquial.
Writers throughout the English-speaking world use learned as the adjective meaning possessing broad, profound knowledge. Incidentally, this sense of learned is pronounced with two syllables: LUR-ned. As a verb and in normal past-participial use, learned is one syllable.
