What is the difference between 'comment' and 'remark'?
Solution 1:
The difference is very subtle; you can use either word. However, in this particular context "comment" sounds better to my ears. It's hard for me to explain why, though. To me, the word "comment" suggests a thoughtful observation (think of the word commentary), while a "remark" could be a completely frivolous statement.
For example,
She commented on my lack of research.
"What an odd color of paper!" she remarked.
You could instead use remarked in the first sentence and commented in the second. But I think it sounds a little better the way I wrote it.
Unfortunately, it's hard to give anything more than a vague reason. Maybe someone else can give you something more concrete.
Solution 2:
The words are not synonyms, however in common usage, people don't know the difference and so use them as they see fit, thinking they are synonymous.
Strictly speaking, a comment is a written note intended as an explanation or criticism of a passage in a book. It is a kind of annotation. The word comes from Latin where it means "interpretation."
To remark is to express briefly as a comment. Remarks are spoken:
"What do you think of my hair?" "Looks great," he remarked.
"I hope he takes a long walk off a short pier," he remarked sarcastically.
Comments are longer, usually in print, and interpret and give extra information. They state an opinion and do so in a longer way than a remark. However, comments can be spoken:
"Mr. President, would you mind commenting on today's deal with the labor union?" In this case, the president would not say "It's great." I suppose he could, but at the level of president, a comment should be lengthy and should help people understand something. If the president were to respond "It's great" my guess would be people present would laugh, as they would be expecting something of more substance than a throw away remark. So in the above example, the president might speak for a few minutes. Comments would not be statements about what the deal was, but would be his interpretation of what the deal means, implications for the job market, and why he supports or doesn't support it.
In your example, in my opinion, it would be better to use comment: She made a helpful comment on my work.
If you look online for definitions of these words, you will find many dictionaries that define the words rather loosely, so it is difficult to distinguish the meaning.
Solution 3:
Webster's Dictionary of Synonyms (1942) places both comment and remark as nouns in a group of similar words that also includes commentary, observation, note, obiter dictum, and descant. Here are the relevant portions of that entry:
Remark, observation, comment, commentary, note, descant, obiter dictum come into comparison when they denote a brief expression intended to enlighten, clarify, express an opinion, or the like. A remark is a more or less casual expression in speech or writing of an opinion or judgment, as of something seen in passing, something read for the first time, something to which one's attention has been called, or the like: the term usually carries no implication of a final or considered judgment; [examples omitted]. ... Comment applies to a remark or an observation made in criticism, in interpretation, or in elucidation of something; [examples omitted].
The updated version of this dictionary—Merriam-Webster's Dictionary of Synonyms (1984)—does not alter its predecessor's discussion of the two words in any meaningful way.
Funk & Wagnalls Standard Handbook of Synonyms, Antonyms, and Prepositions (1947) bundles remark and comment (as nouns) with annotation, note, observation, and utterance:
Remark, annotation, comment, note, observation, utterance
A remark is a saying or brief statement, oral or written, commonly made without much premeditation; a comment is an explanatory or critical remark, as upon some passage in a literary work or or some act or speech in common life.
Evidently, both (or all three) of these dictionaries view remark as being a more extemporaneous or off-the-cuff expression of an opinion or observation, and comment as being a more carefully considered and (perhaps) rigorously argued opinion or observation. This distinction leads me to conclude that Benjamin Harman was correct, in a comment beneath the posted question, to conclude that comment is probably a more suitable word choice than remark to complete the OP's sentence, "She made a helpful ___________ on my work."