The most powerful force in politics, Abraham Lincoln is reputed to have said “are the battalions of time” If this seems an endorsement of the power of the youth to make history, social scientists warn us distinguish between “cohort” effects on the behaviour of youth- changes to the conditions in which a generation of young people are socialised- and”life-cycle” effects- the  extent to which the passage of a generation to adulthood frees forces that change society.