It's got a multitude of meanings bot these are the most common:-be supposed to + infinitive = should Supposed to in this sense means that something should be done because it is the law, the rule or the custom. However, in practice it is often not done: I’m supposed to tidy my room before I go to bed at night, but I always tidy it when I get up in the morning instead. In Germany you’re not supposed to walk on the grass in the parks, but in England you can. I’m supposed to return these books by Friday, but I’m not sure whether I can. In the past tense, it is used to mean that something was planned or intended to happen, but did not happen. Note that in these examples, we can use should have is used as anas an alternative to was supposed to: I was supposed to go to Cuba for a conference last year but then I got ill and couldn’t go. Wasn’t Tom supposed to be here for lunch? I wonder what’s happened to him! I should have gone to Cuba for a conference last year but then I got ill and couldn’t go. Shouldn’t Tom have been here for lunch? I wonder what’s happened to him! Is there a Turkish usage which covers them all?