SWK78

I want to make a film, where both science fiction and fantasy elements are completely equal. In my opinion, with the films i've seen, it hasnt been perfectly done. Each film that attempts it seems to still be missing something, and i can't quite figure it out.

My question to you lot, and hopefully you can help out with this, is

What are the main elements that make a science fiction piece?
What are the main elements that make a fantasy piece?
And do any of you think my above assumption wrong (such that no one has perfectly blended the two genres)?

Please, this is important.
I have wicked ideas, but i dont want to post them on here.

thanks a lot,

SWK78