This OpenStax ancillary resource is @ Rice University under a CC-BY 4.0 International license; it may be reproduced or mod be attributed to OpenStax, Rice University and any changes must be noted. Any images attributed to other sources are simi for reproduction but must be attributed to their sources. 1.3 How Economists Use Theories and Models to Understand Economic Issues One of the most influential economists in modern times was John Maynard Keynes