  Newton's First Law of Motion is typically understood to govern only the
motion of force-free bodies. This paper argues on textual and conceptual
grounds that it is in fact a stronger, more general principle. The First Law
limits the extent to which any body can change its state of motion -- even if
that body is subject to impressed forces. The misunderstanding can be traced
back to an error in the first English translation of Newton's Principia, which
was published a few years after Newton's death.
