Substitution and Simple Sentences

A great deal of attention has been devoted to propositional attitude contexts. Why? A key reason is that the substitution of co-referential names in otherwise identical sentences which ascribe propositional attitudes does not seem to preserve truth conditions. Little attention, however, has been paid to substitution of co-referential names in sentences which do not report propositional attitudes. Why? Because such substitutions are taken to be unproblematic. I will argue, however, that this is not right. There are simple sentences1 which evoke anti-substitution intuitions quite similar to those evoked by attitude-reporting sentences. Imagine that (1) is a truthful description of what happened on a Metropolis street: