Join the following sentences to make one complete sentence without using and, but or so.
They have to go to bed early every night. They are allowed to stay up late on Saturdays.
Topic: Synthesis — clause of contrast
Answer
Although they have to go to bed early every night, they are allowed to stay up late on Saturdays. (Also acceptable: They have to go to bed early every night, whereas they are allowed to stay up late on Saturdays.)
The relationship is CONTRAST — an ordinary rule set against an exception — so ALTHOUGH, THOUGH or EVEN THOUGH is correct.
WHEREAS and WHILE are also available and are worth knowing, because they suit a contrast between two SITUATIONS rather than a frustrated expectation. "They go to bed early on weekdays, WHEREAS they stay up late on Saturdays" is natural English.
The error to avoid: never combine "although" with "but". "Although they go to bed early, BUT they stay up late" is wrong — one conjunction is enough, and using two is among the commonest faults in Indian written English.