I suggest two main ways of interpreting Reid's analysis of the perception of the quality of hardness: (1) Reid endorses two distinct concepts of hardness. The distinction between the two lies in a profoundly different relation between the sensation of hardness and the concept of hardness in each of them. The first concept, which I term as a "sensation-laden concept", is "the quality that arises in us the sensation of hardness." The second concept, which I call a "non-sensational concept", is "the cohesion of the parts of the body with more or less force." (2) Reid is thinking like a developmental psychologist and postulates what I consider as a gradual development from one concept to the other according to which the initial sensation-laden concept of hardness, which we form during our early childhood, gradually develops into a mature non-sensational concept of hardness. Key Terms: Reid; Perception of the quality of hardness; Sensation-laden concept; Non-sensational concept; Psychological development 'It took me four years to paint like Raphael, but a lifetime to paint like a child' (Picasso) When Reid discusses the perception of hardness he brings up a fascinating idea -he says that 'we must become as little children again, if we will be philosophers' (IHM 5.2, 57/120b). 2 This call for the philosopher to learn how to perceive the world the way little children do may be very significant to an understanding of Reid's position regarding his conception of hardness.