substantial performance
under a common law K, if one party has substantially performed, the other party is obligated to perform and complete performance
material breach
occurs when one party’s failure to perform under the K substantially deprives the other party of the benefit they bargained for
time is of the essence clauses
if timely performance is essential as stated in the K, failure to perform by that time is a material breach; arises if one party indicates as a term of the K that performance by a given date is essential