Express performance conditions
1.  Condition – mutually agreed upon promise modifier
2.  Words to look for – “if”, “provided that”, “so long as”, “subject to”, “in             the event that”, “until”, and “on condition that”
3.  Types of express conditions
a.  True condition – an event beyond the influence of either party                     to the K that affects the duty to perform
b.  Condition coupled with an express covenant
i.  Ex – “S covenants to ship the next day and B promises to                     buy only if S ships the next day”
c.  Condition coupled with an implied covenant
i.  Ex – “the sale is conditioned on B obtaining an 8%                         mortgage” – implied covenant of reasonable effort
4.  Standard of compliance
a.  General rule – strict compliance with express conditions
b.  Exception – condition based on the approval of one of the                     contracting parties
i.  Reasonable person standard

5.  Excuse of express conditions
a.  Estoppel – statement by the protected person BEFORE the                         conditioning event was to occur and requires a                         change of position
b.  Waiver – statement by the protected person AFTER the                         conditioning event was to occur and does not require a                     change of position