Yes exactly, and one would intonate it slightly differently by ear depending on what role the note has in the current harmony is the idea. Presume a base note

Yes exactly, and one would intonate it slightly differently by ear depending on what role the note has in the current harmony is the idea. Presume a base note of A is being played and the violin plays a C# functioning as the major third of an A major chord. The ear would want to play the C# justly intonated to the root note A, or maybe a compromise somewhere between equal temperament and just intonation. See for example https://music.stackexchange.com/questions/113812/violin-tuning-equal-temperament-or-just-intonation https://music.stackexchange.com/questions/113812/violin-tuni... there's a lot of nuance. A lot of playing it by ear. :)