Postby bchach08 » June 10th, 2009 8:20 pm
Psy is pretty much right on. From what I have experienced, 想 is used to emphasize that you are think of doing something.
Spoofboy, in your example, "你想吃什么?” vs. “你要吃什么?”, you are saying the same thing where both 想 and 要 are used the same exact way. Both mean, "what do you want to eat?" or "what are you thinking about eating?".
Now, 想, is also used to say “我想吃饭”, stressing that you are hungry and want to eat. Often times, 要 sounds much harsher than 想. Saying “我要吃饭”, is almost like telling somebody you need to eat now and expect to do so.
The two are also very different in that 想 can mean "think" and 要 always is pretty much only used to show a want or need. For instance; “你想什么呢?” means "what are you thinking?", whereas “你要什么呢?” means "what do you want?"
Hope this is right, and hope it helps.