Not implausibly, Arnauld took Descartes’s claim about the ambiguity of the term “idea” to mean that “idea”, or “perception”, refers to one and the same thing, a thing which stands in two different relations. Insofar as it is related to what is known, it is called an idea; insofar as it is related to the mind, it is called a perception. This (act of) perception he took to be related to the mind as a mode of it. It is at this point that Malebranche detected the threat of skepticism. What we know,