to establish a particular mood or character for something The governor's speech was intended to set the tone for the party's national convention next week.
Usage notes: sometimes used with an adjective before tone: The announcement of last month's sales figures set an optimistic tone for the meeting.
if something someone says or does sets the tone for an event or activity, it establishes the way that event or activity will continue, especially the mood of the people involved (often + for ) He was furious when she arrived late, and that set the tone for the whole evening.