According to Reid, "the external senses have a double province; to make us feel and to make us perceive."1 This essay is about the relatione feeling and the perceiving. The central question is, What does Reid thinings, or sensations, are doing in the process of perception? Reid's answer is well-known: sensations function in perception as natural signs of perceived qualities. The answer, however, is not as well-explained, either by Reid or by the secondary literature. Reid's own comments on the sign theory are occasional and their interrelations are neither obvious nor clarified. The literature on the sign theory has yet to recognize and analyze the significance of a cluster of Reid's distinctions—between original and acquired perception, general and particular principles of our constitution, and relative and absolute conceptions.2 This paper aims to put these pieces together into a systematic interpretation of the sign theory that reveals its overall rationale, structure, and coherence. [End Page 329]
2. Where Do Sensations Enter The Account?
Reid lists two constituents of perceptual modes of thought: conception and belief.3 'Conception' is Reid's name for the simple acts of apprehension whereby we get an object in mind in such a way as to affirm or deny something about it.4 Conceptions, per se, neither affirm nor deny; they merely direct thought at objects, and present those objects as being thus and so.5 The objects they present constitute what I call their referential content. The way the objects are presented or described constitutes what I call their descriptive content.6 To produce a mental bearer of truth and falsity, a second mental act is required. Reid's name for this second act is 'belief' or 'judgment', which he characterizes as a simple act of mental affirmation or denial.7 Thus, for Reid, perceiving the tree involves believing that a tree presently exists in one's environment. This belief, in turn, constitutively involves acts of conception and judgment. By acts of conception we apprehend the tree (the referential content) and present or describe it as a presently existing tree (the descriptive content). By acts of judgment we give a mental nod of approval to this way of conceiving the external world.
Apprehension with assent is not unique to perception. We do the same in memory, reasoning, consciousness, and testimony.8 But, Reid explains, the acts [End Page 330] of conception and belief involved in perception have distinctive features. What is affirmed of one and the same object (the descriptive content) differs when we remember and perceive it: in the case of memory we affirm that it existed, in the case of perception we affirm that it exists.9 Conversely, perception and consciousness both affirm that their objects presently exist, but they do not affirm this of the same range of objects (the referential content): in perception we affirm that a mind-independent body or quality presently exists, in consciousness we affirm that a mental operation presently exists.10 The beliefs produced by testimony and reasoning, however, are not distinguished by means of their content. I may be told or infer some of the things I also perceive (e.g., that there is a tree in the quad). To distinguish perception from these types of belief, Reid relies on other features of perceptual belief. Reid maintains that perceptual beliefs are "strong and irresistible," which is not true of the beliefs produced by testimony;11 and that perceptual beliefs are "immediate, and not the effect of reasoning," which is obviously not true of beliefs produced by reasoning (or testimony).12 [End Page 331]
So in perception we apprehend and assent, and we do so in a distinctive way. But that is not all we do. We also feel. Perception is a product of the external senses, and, as Reid explains:
The external senses have a double province; to make us feel and to make us perceive. They furnish us with a variety of sensations, some pleasant, others painful, and others indifferent; at the same time they give us a conception, and an invincible belief of the existence of...