Let's say I work for Toyota. When I introduce myself, are the following sentences OK? Any difference in use?
I work for Toyota.
I work at Toyota.
I work with Toyota.
Let's look at each sentence:
1) "I work for Toyota." (This means that you work for the Toyota Corporation...i.e., the company as a whole. Similar sentences could be: "I work for Volvo," "I work for Mercedes," "I work for General Motors," "I work for Johnson and Johnson," "I work for McDonalds" etc.).
2) "I work at Toyota." (This would mean that the person to whom you were speaking would know of the Toyota dealership at which you work. It connotes familiarity with a certain locale. For example, let's say a worker from a Toyota dealership were eating lunch at a nearby restaurant. When asked by two of the other patrons where it is that he works, he could say: "I work at Toyota, right up the block." He is in essence calling his workplace 'Toyota'....in reality it could be "Toyota of Brooklyn," "Toyota of Austin," "Toyota of London," "Toyota of Paris" etc. [there are many Toyota dealerships around the world].
3) "I work with Toyota." (This could have several meanings: It could mean that you work with the Toyota Corporation: "I work for a firm that specializes in Japanese car parts. We work with Toyota, Mitsubishi, and Isuzu." If one were to say: "I work with Toyotas" [notice the plural], it would mean that he/she were an expert at repairing Toyotas).
I hope this helps.
The above looks confusing, this might make things clearer:
I work for toyota = I am an employee of the toyota company.
I work at Toyota. = I work at the toyota shop. (This doesn't quite work as people don't usually refer to Toyota as a shop, McDonalds would work well instead for this example).
I work with Toyota = I have been contracted to do this job for toyota.
I work for the toyota company.
I work at the Toyota dealership on main street.
I am working with toyota designing a new type of car seat.
Sorry if my explanation was confusing.
I agree with VN's explanation, but one would probably be working at the Toyota dealership, not a Toyota "shop"... just replace it with "dealership" and it should make sense.