92. Material for the exercise of reflection, and so for the excitation of speculative interest, is supplied by whatever in nature, in human affairs, in the structure of languages, and in religion, permits us to discover, or even merely to surmise, a connection according to general laws. But everywhere--the most common school studies, such as elementary arithmetic and grammar not excepted--the pupil encounters concepts, judgments, and inferences. But he clings to the particular, to the familiar, to the sensuous. The abstract is foreign to his mind; even the geometrical figures traced for the eye are to him particular things whose general significance he finds it hard to grasp. The general is to displace individual peculiarities in his thoughts; but in his habitual thought-series the well-known concrete crowds to the front. Of the general there remains in his mind almost nothing beyond the words used to designate it. Called upon to draw an inference, he loses one premise while pondering the next; the teacher is obliged to go back to the beginning again and again, to give examples, and from them lead up to generalizations; to separate and to connect concepts, and by degrees to bring the propositions closer to one another. When the middle terms and extremes have been successfully fused in the premises, they are still only loosely connected at first. The same propositions are repeatedly forgotten, and yet must not be reviewed too many times for fear of killing instead of quickening interest. Since forgetting cannot be prevented, it is wise to abandon for a time a large portion of that into which pupils have gained an insight, but later on to go back to the essentials by other paths. The first preliminary exercises serve their purpose if the particulars are made to reveal the general before generalizations become the material for technical propositions, and before propositions are combined into inference-series. The processes of association (69) must not be omitted between the first pointing out of common features and the systematic teaching of their rational connections.