Freedom-of-movement in thought (the degree to which thought is constrained in its variety as opposed to being free to change) can be empirically dissociated from other well-studied dimensions of thought such as its task-unrelatedness in everyday life setting, but has yet to be studied in a controlled experimental environment. While there are several proposed mechanisms by which thought can become constrained (and therefore less freely moving), none have bene explored empirically. The present study set out to uncover which constructs associated with thought’s task-relatedness were also related to its freedom-of-movement and to test potential mechanisms of constraint. Motivation was within-subjects through a variable-value time-sensitive task and administered experience sampling probes asking participants to self-report the level of freely-moving thought, task-unrelated thought, deliberate control, arousal, and valence they were experiencing. Electrodermal activity and pupillometry were used as an index of physiological arousal in addition to self-reports. When participants were more highly motivated they reported having more constrained and more task-related thoughts, and having greater control over their thoughts. Control fully mediated motivation’s impact on freedom-of-movement of thought, but only partially mediated motivation’s impact on task-unrelated thought. Neither self-report or physiological measures of arousal were impacted by the manipulation, but high levels of both task-unrelated and freely-moving thought were associated with high ratings or self-reported arousal, higher pupillary responses to stimuli and smaller average pupil size, with freely-moving thought being uniquely associated with reduced skin conductance. Additionally, high freely-moving thought ratings were uniquely associated with slower responses, while high task-unrelated thought ratings were uniquely associated with low valence ratings. Overall, these findings support and further extend the previously identified dissociation between task-unrelatedness and freedom-of-movement as two separable dimensions of thought. They indicate that a person’s degree of control over their own thoughts is a crucial determinant of the content and especially the dynamics of that thought, but further work needs to be done to explore what nonconscious factors constrain thought movement.