Look at this sentece: The doctor who was available for appointments is upstairs. If I want to reduce the relative clause I have to delete the relative pronoun and the verb be. So the new sentence: The doctor available for appointments is upstairs. Great! The question is that I have change the sense of the sentence. Grammatically the sentence is fine. But if you compare the previous one with the reduced they do not match each other. The first one tells that the doctor WAS available but right now he is not available. And it also tells that he is right now upstairs. The second one tells that the doctor who IS available is upstairs too. So, what I have got is a different sentece. Please, post your comments. And have fun!