Thomas Reid was the seventeenth century Scottish philosopher who, during his professorship at King's College in Aberdeen, led the attack upon Humean skepticism, then both wide-based and historically deep-rooted in Scottish thought. The responsibility for the success of this attack belongs not only to Reid himself but to them extremely promising minds—whom he affected so profoundly, among them Dugald Stewart, James Beattie, James Gregory, George Campbell, and Alexander Gerard. The school lost favor under the weighty dominance of John Stuart Mill and the British idealists, and Reid's writings, as a result, have suffered from long neglect.
The source of Reid's philosophical strength lies somewhat with his own original thought, but far more solidly with his perceptive thrust into the loopholes of skepticism. The Essays on the Active Powers of the Human Mind is a treatise on ethics, on the human being's performance and motives and freedom. The major points of the Reidan-Humean ethical discourse are as follows:
1. The theory of the origin of ideas. Hume held that ideas derived from sensation or reflection. Though Reid did in fact offer no countertheory, he was the first to point out that Hume substantiated his argument by denying existence to each of the possible alternatives.
2. The freedom of human action. Both Hobbes and Hume had considered the will and the action as the two elements of freedom; the free act, that which is determined by the will, and the unfree act, that done in opposition to the will. Reid defined freedom in terms of the will and its cause. If the agent is the cause of the act of willing, the act is free; if a force other than the agent is the cause of the act of wiling, the act is unfree.
3. The nature of moral judgment. Hume held that these judgments were merely expressions of personal sentiments, for which no objective truth exists. Reid countered that there exists a corpus of moral propositions whose truth is intuitively known, and universally believed, propositions that he referred to as common-sense judgments.