  What are the necessary and sufficient conditions for a proposition to be
called a requirement? In Requirements Engineering research, a proposition is a
requirement if and only if specific grammatical and/or communication conditions
hold. I offer an alternative, that a proposition is a requirement if and only
if specific contractual, economic, and engineering relationships hold. I
introduce and define the concept of "Requirements Contract" which defines these
conditions. I argue that seeing requirements as propositions governed by
specific types of contracts leads to new and interesting questions for the
field, and relates requirements engineering to such topics as economic
incentives, interest alignment, principal agent problem, and decision-making
with incomplete information.
