meirion was noodling in a friends-only post about attraction to people. I commented in reply to that post, but I wanted to say something about it in my own journal too. I suppose the way I see it is that I write things about other people in their journals and about me in my own. Also, this isn't directly relevant to what she said - more of a tangent.
Here follows a list of all of the different ways that I can be attracted to people:
1) Intellectual attraction - when I find someone interesting to talk to, when I am inspired by that person's ideas. I'll actively seek out writing by that person to find out what they're thinking.
2) Emotional attraction - when I find that someone is a good person for me to be around and I'll actively seek them out to spend time with.
3) Physical attraction - when I find someone good-looking in a way that appeals to me personally.
4) Sexual attraction - a more intense version of (3) - perhaps looking at the person makes me feel excited, or smelling their smell percolates my hormones? I think hormones are definitely involved in (4), whereas (5) is purely visual/sensory.
5) Chemistry. I'm not sure what this is. It's something that's present with some people and not with others.
(1) is a form of attraction that I have to everyone whose journals or newsgroup posts I read purely for pleasure rather than for informational purposes. I am certainly intellectually attracted to all of my friends, or else they wouldn't be my friends. (2) likewise.
(3) is different - I don't find all of my friends physically attractive. Some of them are good-looking and some of them aren't. Some of the good-looking ones are good-looking in a way that appeals to my tastes. But I don't actually fancy all of the people that are physically attractive.
I get crushes on people who cause me to have (1), (2) and (3) strongly. I get very strong crushes on people who cause me to experience (1), (2), (3) and (4). Crushes are annoying, because unlike any other kind of relationship they are one-way and un-mutual, and they can get in the way of friendship. I don't like them, but I don't seem to be able to make them go away, so I have to live with them.
Ultimately, though, I think the difference between crush objects and potential partners is that with potential partners, (5) is there. I can't describe what "chemistry" is in this context because it's subjective. All of the other kinds of attraction, (1) to (4) inclusive, can be modified by rational thought. For example, if someone treated me or a friend badly, that could kill my attraction to them. But if there was still chemistry there, the attraction would remain, whatever happened. [I note that the intensely strong chemistry in a relationship I had some years ago is the reason why I would let that person back into my life without a doubt if he decided to make contact with me again. I've only just realised that. Cool.]
I could get into a relationship with someone I had a very strong crush on, provided that the feelings were mutual and we managed to keep things fairly sane and rational. But the only people I'm desperate to get into relationships with are the ones with whom I have strong chemistry. And apart from my existing Relationship, I've only felt that type of connection with one person in the past year or so.