  Reid affirms human beings know what are the intentional contents of their thoughts. If I think about a tree, then I am (defeasibly) justified that I am thinking about a tree. But the Way of Ideas jeopardizes Reid's commitment to the obviousness of our introspective ability to identify what we are thinking about. Like the more familiar veil of perception created by the representational role of ideas (see 3.1 The Way of Ideas and Representational Theories of Perception ), there is also a veil of conception. The seeds of Reid's argument are in Hume's candid remark that, given the Way of Ideas, mental events “seem entirely loose and separate. One event follows another; but we never can observe any tie between them. They seem conjoined, but never connected. ... [T]he necessary conclusion seems to be that we have no idea of connexion or power at all, and that these words are absolutely without any meaning” (Enquiry 7.2.6, 74; see Treatise 1.2.6.8, 67). Hume's causal explanation of reverberating impacts on impressions in the mind does not explain the content of our thoughts. Hume describes his theory of thought as corpuscular because impressions are atomic and separable mental states without any determinate intentional link to anything else. Note that Hume appears to be led to this position by way of his attempt to repurpose Newtonian mechanics, as it applies to bodies, to formulate a science of the mind.