Can I directly use a professor's suggestion? A professor that I have been emailing for advice on graduate school offered to read one of my works for applications (specifically my statement of purpose), and he offered some suggestions using a commenting system on my paper. In the email back to me, he gave some general improvements on things that I could say, but he also crafted a few sentences that would get some of the points across by using quotes.

For example, the email would say something like "You could say something like 'sentence that is applicable to my SOP' to convey your interest in this topic."

Can I use his quoted sentences in my SOP? Was his intention in providing them so that I could directly use them if I chose to?
Yes, you can. If the professor did not want you to use his words verbatim, he'd have described the ideas, but not provided words. Example:


  You could say about how you organized a public talk on this topic to convey your interest.


This gives you an idea of what to write about, but doesn't give you the exact thing to write.

Of course, you don't have to use his words if you think you can express the same idea better in your own words.