A successful defense requires (1) a solid knowledge of the elements of every claim and affirmative defense and (2) experience knowing how judges and juries look at certain defenses. So, then, what are the defenses?
First: Understand the Burden of Proof
The party seeking to enforce the contract has the "burden of proof." It's called a "burden" for a reason. Each element of the claim needs to be proven through competent, credible, reliable evidence by a preponderance of the evidence (more likely than not).
The party seeking to enforce -- and/or defend a claim -- needs to know the elements of a valid contract in PA; these are: a valid offer, acceptance, validating device (consideration), etc. In other words, the Plaintiff must first prove that there was a valid and enforceable agreement. This can be difficult, even if there exists a fully endorsed written agreement that complies with the statute of frauds (requirement of a writing). What are all the terms? The Plaintiff has to the burden to prove exactly how the Defendant breached a specific term, which may be difficult of any of the records of dealings between the parties have gone missing, for example.
The burden then shifts to the defendant to prove that one of the defenses (below) to the contract exists.
Common Defenses