  Reid argues that advocates of the Way of Ideas do not have a plausible solution to this problem. Hume says bluntly that “[E]very simple idea has a simple impression, which resembles it” (Treatise 1.1.1.5, 3), which is a statement of what is known as the Copy Principle: ideas have the content that they do because they are copies, and resemblances, of impressions. Think of a table. For Hume, your thought of a table is derivative and copied from a sensory impression that you have had of that very table. The explanation of the content of the idea of that table thus concerns the contents of your simple impression of the corresponding physical table. The Copy Principle is an exceedingly powerful tool on behalf of the Way of Ideas for a variety of reasons, but Reid is unimpressed with the evidence on its behalf, especially as presented by Hume in Treatise. Reid's response to Hume leads to an argument, which we can call his ‘Sensory Deprivation Argument’.