Does this sentence make sense? One would never say this in English. Instead of 'but', 'and' would be used. Marcus dormit et non scribit. Examples from Orberg which makes more sense (to me, at least): "Mater non te, sed me interrogat.". Or "Rhenus non est fluvius parvus, sed fluvius magnus."
I write this as a question from a beginner, not as one with authority and knowledge in the subject, so please, experts, please clarify!