In principle means true in theory, whatever happens in practice. Agreed in principle, possible in principle, in principle yes.
Agreed in principle is a real stage in a negotiation and means the shape is settled and none of the detail is. It is a warning as much as a concession, since everything difficult is still to come.
1phrasein principleTrue in theory, whatever happens in practice.
“The council agreed in principle to build a new library, but there's no money yet.”
in principle is a qualifier.
In plus principle, from Latin principium, a beginning or foundation.
From in + principle (the noun ultimately from Latin principium). Compare French en principe, German im Prinzip, Dutch in principe, Swedish i princip, Danish i princippet.
Etymology from Wiktionary, CC BY-SA
Practised in Logic & Argument