But attention may be more usefully directed to the extravagantly gratuitous guess involved in hypothesis 3. As a minor point, it is not even carefully worded; for entities which cannot be expressed in terms of matter and motion are common enough without going outside the domain of physics. Light, for instance, and Electricity, have not yet proved amenable, and do not appear likely to be amenable, to purely dynamical theory. Certain phenomena have been reduced to matter and motion,--heat, for instance, and sound, the phenomena of gases and liquids, and all the complexities of astronomy. And in a famous passage Newton expressed an enthusiastic hope that all the phenomena of physics might some day be similarly reduced to the attractive simplicity of the three laws of motion--inertia, acceleration, and stress. And ever since Newton it has been the aim of physics to explain everything in its domain in terms of pure dynamics. The attempt has been only partially successful: the Ether is recalcitrant. But its recalcitrance is not like mere surly obstruction, it is of a helpful and illuminating character, and I shall not be misleading anyone if I cheerfully admit that in some modified and expanded form dynamical theory in mathematical physics has proved itself to be supreme. But does dominance of that kind give to that splendid science--the glory of Britain and of Cambridge--the right to make a gigantic extrapolation and sprawl over all the rest of the Universe, throwing out tentacles even into regions which it has definitely abstracted from its attention or excluded from its ken? There is not a physicist who thinks so. The only people who try to think so are a few enthusiasts of a more speculative habit of thought, who are annoyed with the physicists, from Lord Kelvin downwards, for not agreeing with them. And being unable to gather from competent authority any specific instance in which dynamics has explained a single fact in the region of either life or mind or consciousness or emotion or purpose or will,--because it is known perfectly well that dynamical jurisdiction does not extend into those regions,--these speculators set up as authorities on their own account, and, on the strength of their own expectation, propound the broad and sweeping dogma that nothing in the Universe exists which is not fully expressible in terms of matter and motion. And then, having accustomed themselves to the sound of some such collocation of words, they call upon humanity to shut its eyes to any facts of common experience which render such an assertion ridiculous.