There is a kind of finality in the tone and delivery of a thought that is ending a sequence of ideas. Then the speaker may pause, glance about the audience as if to pull it together, and start again. This pause may be only to give the speaker time to collect his or her thoughts and decide how to start again, but it is a signal of thought completed and a shift to the new idea. These signals indicate the need for notes. Some lecturers make it easier than others to see the organization of their subject matter.
Professors sometimes begin first-year courses with an outline of the lecture on the blackboard.
Main ideas and sub-topics are listed, and the teacher lectures from this outline. Students can copy it and fill in additional statements as the teacher talks. After a few such drills, only the major points are put on the board. The students are expected to recognize and fill in the sub-topics. Soon the teacher stops putting anything on the board, expecting the students to have discovered the lecture form and method.