Brentano's famous thesis of the Intentionality of the Mental was already formulated by Thomas Reid who used it in his campaign against the Locke-Berkeley-Hume Theory of Ideas. Apphed to the case of conceiving the thesis says that to conceive is to conceive something. This principle stands in apparent conflict with the common-sensical view, defended by Reid, that we can conceive what does not exist. Both principles, it is argued, are plausible and should be retained. The problem is how to resolve (...) the apparent contradiction. Reid's way out of the dilemma is clarified by contrasting it with less satisfactory solutions. (shrink)