Definite Article Or Indefinite Article?

purple file 704Is it appropriate to say "(by) the author who has taught 7 million people" in this context?

It needs a comma pretty badly: Core concepts explained by the author, who has taught 7 million people

purple file 704I guess the noun phrase should be replaced by "an author who has taught 7 million people." Am I right?

That would work a little better than the version without a comma, but it defeats the reason for saying "author" in the first place. He is the author of this very book, which is the whole point of mentioning the fact. If you say "an", it leaves open the possibility that the proffered explanations are presented by someone who is not the author of this book. But I do see your problem, and I agree that something needs to be done.

Thank you. I agree that if you leave the definite article, you need a comma before the relative clause.

Thank you. I agree that the use of the word "author" in the title is not without problems.

purple file 704I guess the noun phrase should be replaced by "an author who has taught 7 million people." Am I right?

That's what I would have written.

CJ

Thank you.

AlpheccaStars

anonymousI guess the noun phrase should be replaced by "an author who has taught 7 million people." Am I right? Thank you.

The definite article is used because there is one specific, definite author of the book.
However, the relative clause is non-defining (only informational) so a comma is required.

The Definitive English Grammar Guide: Core concepts explained by the author, who has taught 7 million people

I agree that is not semantically restrictive, but it is integrated, though, so no comma is required.

The reason for expressing it an integrated relative is that it has crucial relevance to the rest of the message. It is probably because the author has taught seven million people that he/she is able to write the book.

anonymousI agree that is not semantically restrictive, but it is integrated, though, so no comma is required.

"integrated" is not a grammatical concept. Non-restrictive (non-defining) is.

https://owl.purdue.edu/owl/general_writing/grammar/relative_pronouns/relative_pronouns_in_non_defining_clauses.html

https://learnenglish.britishcouncil.org/grammar/b1-b2-grammar/relative-clauses-non-defining-relative-clauses

So there are two choices

1. - use the indefinite article without a comma (an author who has taught 7 million people)

I find it rather for the writer to be cited in the title of their own book... usually it would be in a review of the book, or perhaps in a subtitle.

2. - use the definite article with the comma. (the author, who has taught 7 million people)

If the author's name is used, the comma is required.

The Definitive English Grammar Guide: Core concepts explained by Amy Johnson, who has taught 7 million people