Full Idea
Although one can separate 'in thought' a direction from any line of which it is the direction, one cannot conceive of a direction existing in the absence of any line possessing that direction.
Gist of Idea
You can think of a direction without a line, but a direction existing with no lines is inconceivable
Source
E.J. Lowe (The Possibility of Metaphysics [1998], 10.3)
Book Reference
Lowe,E.J.: 'The Possibility of Metaphysics' [OUP 2001], p.216
A Reaction
Intriguing. If I ask you to imagine a line going in a certain direction, don't you need the direction before you can think of the line? 'That line is going in the wrong direction'. Maybe abstract ideas only exist 'in thought'. Lowe is a realist here.