 Although Frege had a formal system in which the open sentence \(Fx\) doesn’t logically imply \(Gx\), he takes logical consequence to be a relation among thoughts. He wouldn’t answer the question, of whether one thought is a logical consequence of another, solely by looking at the form of the sentences that express them, but rather by looking at the content of those sentences. Given the meaning (content) that ‘nightmare’ and ‘dream’ in fact have, “\(x\) had a dream” is a logical consequence of “\(x\) had a nightmare”, for having a nightmare, i.e., having a bad dream, logically implies having a dream. So, for Frege, this would clearly be a case of logical consequence.