A vs. One -
“I would like a sandwich.” This simply communicates the wish for an undefined sandwich.
“I would like one sandwich.” This seems to emphasize the number of sandwiches you want- not two or three, but one.
What is the proper usage? To my ear, both sound technically correct, but using “a” sounds more fluent and native. Using “one” here sounds kind of stilted and over precise or something.
Can anyone offer me the Straight Dope on this?
Thanks in advance,
BB
Your interpretation is correct. The use of ‘one’ in the second sentence confirms the quality desired whereas the use of ‘a’ in the first sentence merely confirms a desire for said sandwich.
Both sound idiomatic to me. The only difference is emphasis.
They’re both technically correct, in that particular context. What are you trying to figure out here? As far as how one would “normally” talk, “a sandwich” is certainly more conversational, but both would accomplish the same goal if ordering a sandwich at a deli or something.
“One would like a sandwich”. 
Both are correct, as others have said, but they mean slightly different things and the context dictates what is more appropriate.
“What do you want for lunch, Bamboo Boy?”
“I’d like a sandwich.”
“Welcome to Subway. What can I get you?”
“I’d like one sandwich to go, please.”
In the latter case, you could substitute “a”, but I, as a native English speaker," would say “one.”
I use context to some extent for deciding which usage to go with. By default, I use “a”, but sometimes use “one” when other quantities are involved, particularly if I’m deviating from a typical combination of quantities.
“I would like a sandwich.”
“I would like a sandwich and a soda.”
“I would like one sandwich and two sodas.”
In the third example, there’s a chance I will be breaking the listener’s expectation that one sandwich will be associated with one drink. Emphasizing the quantities may help clarify the intent slightly. If, on the other hand, I were asking for a food item that people often order more than one of in conjunction with a single drink, I would generally use “a”, because the situation seems less likely to cause confusion.
“I would like two biscuits and a cup of tea.”
None of this is at all prescriptive, however–you would swap “one” and “a” around however you like, and it would still be correct. My native language is the southern U.S. dialect of English, for whatever it’s worth.
English is my native language too, FTR. Thanks for the input, I just wanted to see if other people out there in Cyberland thought more or less the same thing I did about this. (They did.)
I’m teaching a Russian woman English somewhat informally and she asked me the difference and when to use what. I was hard pressed to come up with a concrete answer.
Thanks again for the input!
-BB