Whether it was physiological or psychological didn't matter at this point.
He pushed the sensualistic principles of Condillac to their last consequences, being in full agreement with the materialistic views of Cabanis, though the attention of the latter was devoted more to the physiological, that of Tracy to the psychological or "ideological" side of man.
His work embraces in its scope many psychological and more strictly metaphysical discussions, but it is chiefly in connexion with ethics that Tucker's speculations are remembered.
The fundamental principle of his philosophy was that truth must be sought not in metaphysical or a priori abstractions but in psychological investigation, and further that this investigation cannot confine itself successfully to the individual consciousness, but must be devoted primarily to society as a whole.
Accordingly Aquinas prepared himself on this side by commentaries on Aristotle's De Inter pretatione, on his Posterior Analytics, on the Metaphysics, the Physics, the De Anima, and on Aristotle's other psychological and physical writings, each commentary having for its aim to lay hold of the material and grasp the method contained and employed in each treatise.