Marked and Unmarked themes

The unmarked English language option is always to equate the Theme with the subject. The information focus, where the important New information is stored, generally falls at the end of the clause:
THE TWO INDIANS stood waiting
NICK AND HIS FATHER went into the stern of the boat.
Also common, and thus unmarked, as Themes are subjects with complex modifications or when they contained noun phrases.
THE INDIAN WHO WAS ROWING THEM was working very hard.
THE TRIAL, AND THE INVESTIGATION THAT LED TO IT, lasted two years.
Marked theme means that the theme appears in an atypical or unusual position. In terms of Given/new and information focus, many marked themes present some New information.
An analysis of the theme structure of both marked and unmarked clauses reveals how information is presented in typical English constructions as well as the communicative purposes of the writer. A marked theme enables the writer to present the message in the way he wants, by foregrounding different information from the unmarked option:
the passive voice __ Only the best tennis is played at Wimbledon
the cleft sentence __ It was Bill who scored goal
the pseudo-cleft sentence __ What Did Bill was galvanise the rest of the team
an embedded clause as subject __ That Mary would come back to London was never in doubt
the thematisation of objects and adverbs __ Aruba is where I go on vacation for two weeks every year.