distinguish, differentiate, discriminate, and demarcate can mean, in common, to point out or mark the differences between things that are or seem to be very much and often confusingly alike. distinguish implies a reason for confusion as between two things having an extremely close relationship or connection

nothing more profoundly distinguishes the Hellenic from the modern view of life than the estimate in which women were held by the Greeks — G.L.Dickinson
he must be taught to distinguish between the truth and his imagination — Mary Austin
a child under four will hardly distinguish between yesterday and a week ago — Bertrand Russell
Dr. Dunham distinguished between the terms public relations and publicity — T.F.Reidy

differentiate implies the possession of a distinguishing character or characters or the ascertainment of the differences between things easily confused

his immaculate appearance differentiates him from his fellow workers
classes small enough to enable the teacher to differentiate the strong and the willing from the sluggards — C.H.Grandgent
he differentiates industrial, political, and moral activities — D.S.Robinson

discriminate can imply the possession of obvious distinguishing characteristics

his gift of fine oratory discriminates him from other statesmen

but usually implies the power to discern differences, often slight, between similar things

irritated by the wasp's inability to discriminate a house from a tree — E.K.Brown
no dictionary discriminates perfectly among these finely shaded distinctions in trade vocabularies — Ben Riker
demarcate, implying the literal setting of boundaries, can be used to suggest a distinguishing between things as if by marking them off
how shall we demarcate reproduction from growth — G.H.Lewes