Today I wrote the following to a colleague

You may want to clarify your statement that a response to your survey "is both confidential and anonymous." If it is confidential, it is not anonymous because at least one person knows who wrote what responses, it's just that they are not telling. If it is anonymous there is no need for confidentiality because no one other that the subject knows what responses they wrote.

So my question is is the survey anonymous or confidential?

Haven't gotten a response yet --can't wait to see what it will be.