著者 and 著作: An Author to Question and Three Works Borrowed
Compare the author one could question or who records observations with borrowed works and later writings. Distinguish person, work, opportunity, and the number of books.
A person one could question and a person recording experience
著者 (ちょしゃ) means author. 「講演の後で著者に質問する機会がありました。」 — “I had an opportunity to ask the author a question after the lecture.” 機会がありました reports an opportunity after the lecture, without establishing that a question was asked or answered.
「この本の著者は自然観察の経験を丁寧に記しています。」 — “The book's author carefully records experiences observing nature.” The person recording the nature-observation experiences is the book's author. 著者 identifies the person who wrote the book here.
The number of works and feelings expressed in writing
著作 (ちょさく) means a work or writing. 「図書館でその研究者の著作を三冊借りた。」 — “I borrowed three works by the researcher from the library.” 三冊 counts three borrowed works by the researcher, rather than three authors.
「晩年の著作には故郷への思いが色濃く表れている。」 — “His later writings strongly reflect his feelings for his hometown.” The later writings reflect feelings for home. Those expressed feelings do not report an actual return to the hometown.
The person referred to and the work referred to
著者に質問する identifies the person to whom a question could be addressed. 著作を三冊借りた identifies the works borrowed. A count of works does not become a count of authors.
Separate 著者 as the person from 著作 as the works in these examples. The opportunity differs from asking, and feelings expressed in writing differ from a completed return.
Does borrowing three of the researcher's 著作 mean there are three 著者?
Show the answer and why
No. Three is the number of borrowed works, and their author is the researcher. The separate opportunity to question an author after a lecture also does not establish that a question was asked or answered.