Swerve and Impulse

Behavior that is more random and spontaneous than Will is Impulse.  Now, on a Spinozist analysis, Impulse is merely the effect of an external influence, and is unexpected for that reason alone.  However, according to Dewey, Impulse is in itself "plastic", i. e.formless, functioning primarily to break from established Habit, with its eventual direction contingent.  This he presents without referencing Lucretius; regardless, if he is correct, then Swerve is essentially a Psychological, not a Physicist, principle, from which Will is derived, and from which it derives its 'Free' character.