Complex sentence: Under these assumptions, Say's law states that there cannot be a general glut, which, Keynesians conclude, means that there cannot be a persistent state where demand is generally less than productive capacity and high unemployment results.
Split into simpler sentences: Under these assumptions, Say's law states that there cannot be a general glut. Keynesians therefore concluded that there cannot be a persistent state where demand is generally less than productive capacity and high unemployment results.