play along
To pretend to agree or join in to keep things smooth.
To play along means to cooperate with something or pretend to agree, even when you might have doubts or know better. When your little sister insists she's a princess and you play along by calling her “Your Majesty,” you're going with her game to make her happy. When a friend tells an obviously exaggerated story about catching a huge fish, you might play along by asking impressed questions, even though you suspect the fish wasn't quite that enormous.
Playing along often means temporarily setting aside your own perspective to help something work smoothly. If your teacher starts a creative writing exercise by saying, “Imagine we've traveled back to ancient Rome,” the whole class needs to play along with that premise for the activity to succeed.
The phrase can carry different tones depending on the situation. Sometimes it's generous and kind, like when you play along with a younger child's imagination. Other times it might feel like you're being cautious or strategic, like when you play along with a plan you're not entirely sure about while you wait to see how things develop. In detective stories, a character might play along with a villain's scheme to gather information, pretending to be fooled while actually staying alert.