 Descartes’ Principles of Philosophy also presents his most extensive discussion of the phenomena of motion, which is defined as “the transfer of one piece of matter or of one body, from the neighborhood of those bodies immediately contiguous to it and considered at rest, into the neighborhood of others” (Pr II 25). Descartes attempts to distinguish his “proper” conception of motion, as a change of the “neighborhood” of contiguous bodies, from the common or “vulgar” conception of motion, which is change of internal place (Pr II 10–15, 24–28). The surface of these containing bodies (that border the contained body) is also called the “external place” of the contained body. Descartes notes that the vulgar concept of motion allows a body to simultaneously take part in many (possibly contradictory) motions, as when a sitting passenger on a ship views himself as at rest relative to the parts of the ship, but not at rest relative to the shore (Pr II 24). Yet, when motion is viewed as a translation of the contiguous neighborhood, a body can only partake in one motion, which dispels the apparent contradiction (since the body must either be at rest, or in translation away from, its contiguous neighborhood).