William James, A Pluralistic Universe
“ If directed, it shows tendency. The tendency may or may not be resisted. If not, we call the activity immanent, as when a body moves in empty space by its momentum, or our thoughts wander at their own sweet will. If resistance is met, its agent complicates the situation. If now, in spite of resistance, the original tendency continues, effort makes its appearance, and along with effort, strain or squeeze. ”
