One of his final works, which included such chapters as "The Sense of Duty," contrasted "speculative power" with "active power."  
This thinker posited that self-consciousness about deliberating whether or not to do something evidences the existence of moral liberty.  His first publication argued against the ability to measure virtue and was titled "An Essay on Quantity."  This philosopher's core beliefs were initially popularized in the Essay on Truth, a simplified take on his ideas by James Beattie.  One of his final works, which included such chapters as "The Sense of Duty," contrasted "speculative power" with "active power."  This student of George Turnbull, rejected the empiricist reliance on ideas as the basis of knowledge, instead he argued that sensations of an object's primary qualities offer up natural signs to the mind, which are interpreted like words.  For 10 points, identify this philosopher whose works include Essays on the Intellectual Powers of Man and Enquiry Into the Mind on the Principles of Common Sense.
This thinker posited that self-consciousness about deliberating whether or not to do something evidences the existence of moral liberty.  
Thomas Reid