Supposing the agreement and its breach to be prima facie capable of proof against the defendant, he may, by way of defence to the action, show, either that the agreement was originally invalid, or that it has since its execution ceased to be binding, or that satisfaction has been made for its breach.

For instance, he may show that, at the time of the execution of the contract, he was under some personal incapacity to contract (h); or was under duress (i); or was fraudulently induced to enter into it (k); or that it was entered into for or with reference to some unlawful purpose (l).

So, admitting its original validity, he may show that it has been since avoided by having without his concurrence been altered by the plaintiff in a material part (m); or by a waiver in writing duly signed by the plaintiff (n) before the breach which is relied on in the action (o): Sir E. Sugden holds it to be the better opinion that a verbal waiver of a written agreement is no defence at Law (p); but the reported cases, although they leave the point doubtful, seem rather to lead to a contrary conclusion (q): and the Statute of Frauds seems merely to take away the remedy by action in the case of a verbal contract, without saying anything to affect the common-law right of waiving by word of mouth a contract not under seal.

Grounds of defence to action on contract duly executed.

Original invalidity of contract; or subsequent waiver

(f) See Street v. Brown, 6 Taunt. 302.

(g) See Travis v. Collins, 2 Cro. & Jer. 625; Neale v. Swind, 2 Cro. & Jer. 278. See Mr. Tilsley's remarks, Tils. on S. L. p. 386.

(h) Supra, Ch. I.

(i) Bac. Abr. tit. Duress.

(k) See Haigh v. Be La Cour, 3 Camp. 319; Emanuel v. Bane, ib. 299; Solomon v. Turner, 1 Stark. 51; Hutchinson v. Morly, 7 Scott, 341; Cornfoot v. Fowke, 6 Mee. & W. 358; actual fraud in the agent is the same as fraud in the principal, Doe d. Willis v. Martin, 4 Durn. & E. 39; Wilson v. Fuller, 3 Q. B. 68.

(l) Bartlett v. Vinor, Carth. 252; Langton v. Hughes, 1 M. & S. 596; Be Begnis v. Armistead, 10 Bing. 107; Gas Light Company v. Turner, 8 Scott, 609; Ritchie v. Smith, 6 C. B. 462; and see Ewing v. Osbaldiston, 2 Myl. & Cr. 53; and note, anything to which a Statute attaches a penalty is unlawful, although not expressly prohibited; and see Appleton v. Campbell, 2 Car. & P. 347.

So, the defendant, admitting the agreement and its breach, may show that the plaintiff has executed a release under seal; or has accepted something in satisfaction of the breach (r); or has already recovered damages in an action upon the agreement (s); or that the action has not been brought within the time allowed by the Statutes of Limitation.