Final answer:
Keynesian theories, developed by John Maynard Keynes, advocate for active government intervention in the economy, particularly during economic downturns, by adjusting fiscal policies to stimulate growth or curb inflation.
Step-by-step explanation:
The statement about Keynes' original theories that is true is that they focused on the importance of government intervention in the economy. Keynes, a notable British economist, wrote during the Great Depression and proposed that government could use fiscal and monetary measures to mitigate the effects of economic downturns. This approach recommended employing government spending and tax policies proactively to manage aggregate demand within the economy, providing stimuli during recessions and tempering inflation during boom periods.
Keynesian economics thus does not support a laissez-faire approach nor does it rely on the assumption of perfect competition in markets. Instead, it sees a strategic and often crucial role for the government in attempting to stabilize market fluctuations and sustain employment levels through active fiscal policies.