When to change bow direction on the violin?!

The answer is simple. Unless otherwise marked, you should change bow directions on every note. There are 2 markings that would tell us otherwise.

Number One: the slur (seen below).

A slur indicates that every note beneath it should be played under the same bow (ie all down up or all up bow). A slur by itself means all of the notes should be played smoothly. This is a bow stroke called legato.

If there are dashes or lines under or over the notes, there should be a slight space between each note. This bow stroke is called portato.

If there are dots under or over the notes, there should be a clear space between each one. This bow stroke is called up or down bow staccato.

Number Two: two or more consecutive bow markings (seen below).

These markings indicate that both of those notes should be played up bow.

Unless you see either of these indicators, change your violin bow direction on each note.