William James, The Principles of Psychology, Volume 2…
“ If we admit, therefore, that our thoughts exist, we ought to admit that they exist after the fashion in which they appear, as things, namely, that supervene upon each other, sometimes with effort and sometimes with ease; the only questions being, is the effort where it exists a fixed function of the object, which the latter imposes on the thought? or is it such an independent 'variable' that with a constant object more or less of it may be made? ”
