予習 and 自習: advance timing and a self-study method
Compare preparing tomorrow's text with studying independently after school or organizing problems during self-study time. Read timing and method as dimensions that can apply together.
Timing before a lesson and a way of studying
予習 (よしゅう) means studying material in advance of a lesson, while 自習 (じしゅう) means self-study. The first focuses on timing relative to a lesson; the second focuses on how the studying is done.
If someone studies tomorrow's text independently beforehand, both descriptions can apply. This combines two dimensions in a hypothetical activity, rather than making preparation and self-study separate, successive stages.
Preparation and easier understanding
「明日の授業で読む文章を予習した。」 — “I studied the text for tomorrow's class in advance.” The advance study is reported as completed. What was completed was preparation of the text, rather than attendance at tomorrow's class.
「十分に予習しておくと先生の説明が分かりやすい。」 — “If you study thoroughly in advance, the teacher's explanation is easier to understand.” 十分に予習しておくと states a condition involving thorough preparation. Easier understanding of the explanation does not report that understanding has already been completed.
Study after school and organizing problems
「放課後に図書室で一時間自習した。」 — “I studied on my own for an hour in the library after school.” The sentence reports an hour of self-study in the library after school. Its stated time and place do not require every self-study session to use that schedule or occur in an otherwise empty room.
「自習の時間に分からない問題を整理した。」 — “During self-study time, I organized the problems I did not understand.” The reported action during self-study is organizing problems that were not understood. Organizing them does not establish that all were solved or that advance preparation is impossible during self-study time.
If someone independently studies tomorrow's class text beforehand, can both 予習 and 自習 describe that activity?
Show the answer and why
Yes. Studying before the relevant lesson fits the timing of 予習, and studying independently fits the method of 自習. This hypothetical combination does not identify the separate supplied examples as one person's single event.