Is it ethical to use a proofreader for your thesis?
This question comes up constantly, usually from a student who's worried that getting help with language somehow crosses the same line as getting help with results. It doesn't -- but the distinction is worth spelling out clearly, because the line does exist somewhere.
What's standard practice
Language editing -- correcting grammar, improving clarity, formatting citations -- is explicitly permitted by the vast majority of universities and journals. It doesn't change your findings, your methods, or your argument; it changes how clearly those things are expressed. Most style guides for graduate research (including guidance from bodies like the Council of Science Editors) draw the same line: editing language is acceptable, editing content is not.
Where the line actually sits
The distinction is authorship, not effort. A proofreader fixing your sentence structure hasn't contributed an idea, a result, or an argument -- you did that. A proofreader (or an AI tool) rewriting your discussion section to make a stronger claim than your data supports has crossed into content, and that's a different, real problem.
Check your institution's specific policy
"Standard practice" isn't the same as "your specific university's written policy," and policies vary -- some require a disclosure statement, some don't allow professional editing at all for certain assessed pieces. Check your handbook or ask your supervisor before commissioning an edit if you're at all unsure. Any editor should be willing to work within whatever those rules require.
What this looks like in practice
A properly scoped edit returns your document with tracked changes, so you can see exactly what was altered and why -- nothing hidden, nothing added that wasn't already your own thinking. That's the standard I hold every edit to; see how it works for the process.