Everything replied to this thread is wrong.

You're supposed to play the notes in accordance tho their context. For chords and double stops, you use either just intonation or equal temperament - otherwise they'll sound off. For solo melodies, you use mostly Pythagorean tuning and adjust expressively when needed. When playing in a polyphonic ensemble, you choose the temperament that rings the best with the rest of the ensemble - usually just intonation or equal temperament.

The main difference between Pythagorean tuning and just intonation is that within just intonation the 3rds and 6ths are tuned to perfect, small fractions, while Pythagorean tuning relies on stacked fifths and makes those intervals sour. That's why when soloing double stops you often apply just intonation over staying strictly in Pythagorean.

It's violin, not piano. You're not supposed to play it like piano. You're free, and expected, to adjust your intonation in accordance to the piece and performance context.

Many recommendations regarding intonation replied to this thread are wrong.

You're supposed to play the notes in accordance tho their context. For chords and double stops, you use either just intonation or equal temperament - otherwise they'll sound off. For solo melodies, you use mostly Pythagorean tuning and adjust expressively when needed. When playing in a polyphonic ensemble, you choose the temperament that rings the best with the rest of the ensemble - usually just intonation or equal temperament.

The main difference between Pythagorean tuning and just intonation is that within just intonation the 3rds and 6ths are tuned to perfect, small fractions, while Pythagorean tuning relies on stacked fifths and makes those intervals sour. That's why when soloing double stops you often apply just intonation over staying strictly in Pythagorean.

It's violin, not piano. You're not supposed to play it like piano. You're free, and expected, to adjust your intonation in accordance to the piece and performance context.