There are two ways of interpreting this claim, and this ambiguity tracks two distinct positions in the secondary literature on Reid.
On the one hand, sensations, for Reid, can be understood to not have objects at all: as such, this mental operation is distinct from all others.
Just like perceptions and memories, sensations are constituted by two other ingredients: a conception of the object, and a belief that the object exists, except, in the case of sensation, this object is the sensation itself, not an external object like trees, frogs, or human beings.
A consequence of understanding Reid as saying that sensations do not have any kind of objects is to think that he is a precursor of “adverbial” theories of sensation.
He contends that going back to the principles of common sense will help deal with the problems engendered by the so-called “skeptical views" of his predecessors: Descartes, Locke, Berkeley, and Hume.
He argues that “the way of ideas” generates undue uncertainty in the theory of knowledge.Rejecting the notion that ideas are the direct object of the mind’s awareness, Reid substituted a view of perception in which sensations “suggest” material objects.For him, this ambiguous assertion solved the problem.Although careful introspective observation will reveal that sensations do not usually occur on their own, but are almost always accompanied by perceptions, Reid is pointing out that a clear-cut distinction between sensation and perception exists and should be accounted for.This distinction has to do primarily with the specific roles sensations and perceptions play in the knowledge of the external world.In philosophy of mind, Reid is most celebrated today for the arguments he gave in support of the position known as direct realism, which, at its most basic, states that the primary objects of sense perception are physical objects, not ideas in human minds.However, Reid’s philosophy of mind neither begins nor ends with perception.He is a worthy successor of Newton, in that he believes that the scientific method is the right way of investigating the nature of mind.Reid characterized the scientific method mainly by trial and error, and by setting up experiments and drawing general conclusions from them.But a person can never be mistaken about a feeling that particular person has: whenever someone has a headache, that ache is real and it is that person’s and it is exactly as that person is feeling it.On the other hand, that passage has been read as saying that sensations take themselves as objects; Reid, in this interpretation, would subscribe to a reflexive view of sensations.