Suppose we want to make a question from
To be in love means X
where X is some phrase.
People usually say
What does it mean to be in love?
What is the role of "it" here? (a dummy subject? If yes, how could the affirmative sentence be rephrased in a way which includes it?) The subject of the affirmative sentence is "to be in love". Shouldn't it appear directly after the auxiliary verb in the question? like this:
What does to be in love mean?
You have already phrased the question without using "it" - but look at it another way:
You say you are in love. What does that mean?
You can use a pronoun like "it" or "that" to refer to a thing previously mentioned or easily identified. In my example above it has been established we are talking about being "in love" so it is clear when you next ask "what does that mean" you are referring back to the same thing.
Likewise, when you ask:
What does it mean to be in love?
It is clear that "it" means "to be in love". There is some benefit to phrasing it this way, as the auxiliary verb "to be" makes it clear that you are talking about the concept of being in love, which could prompt a much broader, more philosophical answer than asking "What does 'in love' mean?" which could merely require a dictionary definition.
