It will be readily admitted that often our thinking is so loose and disjointed that its component parts resemble the liquid more than the chain, whereas our best thinking—namely, that which leads to a goal in the shape of a trustworthy conclusion—resembles a train of cars in which motive power is derived not from steam, but from a conscious expenditure of will-power. The teacher may perform the triple function of fireman, engineer, and switch-tender, supplying the fuel for the process, regulating the speed, and directing it along the lines of track which lead to the desired goal. It is as natural for a pupil to think as it is for a stream to flow towards the ocean. The stream may run shallow if no supply of water is received from the outside. It is the mission of the teacher to keep up the supply, to remove as far as possible the obstructions which are likely to throw the current of thought into unexpected channels. It is a peculiarity of this current of thinking that it is cognitive, or possesses the function of knowing. Human thought resembles the stream in seemingly taking up and carrying what was not a part of itself. Just as the stream of water carries minerals in solution as well as silt, sand, pebbles, and even heavier objects, so the stream of thought appears to lay hold of objects and to carry them as part of itself. Here, however, the strings of the analogy break. The stream of thought is in the mind; the objects with which it deals are outside of the mind. Mental pictures of these objects float in the stream of thought as objects on the bank of a river are mirrored in its waters; yet the parallel is not complete, because the mind may turn the eye upon itself and make what is thus seen the object of thought. This turning upon itself may be likened to eddies in the stream. But even when the mind thus turns back upon itself and views its own states and activities, these are regarded as objective, as related to the thinking process very much like the objects of knowledge in the external world.
Another important phase of thinking finds no likeness in any of the figures of speech above referred to. The mind meets certain objects of thought on which it seems to tarry or fasten itself. This has led some writers to deny that the stream of thought is a continuous current. This view causes undue stress to be laid upon the material of thought, and leads the teacher to undervalue his function as directing guide in teaching pupils to think. Even Professor Bain claims that,—