Outlines are of three kinds: those that show the topic relations by division into indented headings; those that show the sequence of paragraphs by statement of the topic sentence; and those that combine these two forms. The primary object of the first form, which is illustrated by the first outline of "An Idyl of the Honey-Bee" which follows, is to aid in the thinking, to plot out the ground and to group the material. In this first outline a glance at the five main headings makes the plan of the essay at once apparent--first a statement of the effect of bees upon us; then an account of a hunt; then some specific examples to drive things home; then some special directions that might be overlooked, and finally a tribute to the joy of the hunting. The benefit of this kind of outline is that the general relationships among topics are made clear, the large divisions of thought appear, and the writer can with comparative ease tell whether he has covered the subject, and whether he has chosen the best order of thought. It avoids the invertebrate flow of thought that is unaware of structure. In other words, it is of value chiefly to the thinking. It does not show which topics shall be grouped into paragraphs together, and it does not, of course, phrase the topic sentences, usually. In such an outline care should be taken to make each heading a complete sentence, and to make headings that are of the same rank fairly parallel in structure of expression unless this interferes with the tone of the heading. For example, A, B, and C under III are made similar in structure since they bear the same general relation to III.
The second type of outline, that in which a list of the topic sentences is given, and which is illustrated by the second outline of "An Idyl of the Honey-Bee" which follows, is of value, especially if used with an outline of the first type, in that it shows just how much of the thought should go into the various paragraphs, and thereby establishes the divisions of expression. Comparison of the two outlines of "An Idyl of the Honey-Bee" will show that paragraph 5 in the second outline includes all the material in the four headings, 2, a, 1´, and b, under II in the first outline. Now for the writer to know beforehand how he intends to divide his material into paragraphs is of great value; otherwise he might be giving to some comparatively minor point--which for the moment assumes interest for him--a separate paragraph, as if, for example, Mr. Burroughs had dwelt at length on the interesting location of trees on ledges. In other words, this second kind of outline is valuable chiefly in its arrangement and placing of material. Its service in making the original choice is not so immediately apparent. It has also the advantage that it indicates pretty well what kind of expression is to be used in the expanded form.