The concept of Motion has been the subject of constant discussion by physicists and mathematicians for centuries, and in recent years the classical kinematics has been profoundly modified, owing to circumstances that have arisen within the region of Physics itself. Yet some of the chief exponents of the General Theory of Relativity, which is the latest phase of kinematics, use language which seems to imply a thoroughly Absolute Theory. To many scientific readers they will of course be perfectly familiar, but it will do no harm to the reader who is primarily a philosopher to put himself au courant with the present position in Physics before going further. Absolute Space, Time, and Motion have all the appearance of being mathematical devices, and not substantial constituents of nature, and a theory is to be preferred which reduces such mathematical scaffolding to a minimum, provided of course that it is adequate to all the facts with which it professes to deal.