"What makes each of us unique are our principles" or "What makes each of us unique is our principles"?
***** NOT A TEACHER *****
Hello, Johnnglsh.
(1) Some experts say that "what" is always singular ("The thing that").
So your second sentence would be correct.
(2) Today most experts say that "what" may be singular ("The thing
that") or plural ("The thingS that").
(3) I may be wrong, but I think that your sentence is "easy" to
analyze:
(a) The writer said: What makeS. '
(b) Therefore, s/he was thinking of "the thing (singular) that."
(c) So your sentence is something like:
The thing (that makes each of us unique) IS our principles.
(i) The thing IS/ NEVER: The thing are.
(4) BUT please remember two things:
(a) Sometimes "what" is plural. ("The thingS are")
(b) It is not always easy to know whether to use "is" or "are."
(Even the experts often disagree.)
(c) Even though "is" is the "correct" answer to your question,
there are some (many?) native speakers who would use "are"
because it sounds "better" or "more natural."
(d) Here are two sentences from a very popular English usage book:
(I changed the example a little bit)
(i) What worries restaurant owners more ____ customers like John Doe.
(a) The usage book says that the "correct" answer is "is," but that
"are" sounds more "modern." The writer of that book says that "are"
in that sentence is NOT "wrong." Some books would say "are" IS wrong.
You are a learner. So you should probably follow the "rule"
and use "is" in your sentence. Remember: sometimes the "rule"
will require you to use "are." If you find other confusing "what"
sentences, be sure to post them here so that people can discuss them.
***** Thank you *****