Lach v. Cahill, 138 Conn. 418, 421 (1951)
A condition precedent is a fact or event which the parties intend must exist or take place before there is a right to performance. If the condition precedent is not fulfilled the contract is not enforceable.
Platt Pacific, Inc. v. Andelson, 6 Cal. 4th 307 (1993)
Private arbitration is a matter of agreement between the parties and is governed by contract law. (See, e.g., Moncharsh v. Heily Blase (1992) 3 Cal.4th 1, 8 [10 Cal.Rptr.2d 183, 832 P.2d 899]; Ericksen, Arbuthnot, McCarthy, Kearney Walsh, Inc. v. 100 Oak Street (1983) 35 Cal.3d 312, 323 [197 Cal.Rptr. 581, 673 P.2d 251]; Code Civ. Proc., §1280 et seq.) (3a) Under the law of contracts, parties may expressly agree that a right or duty is conditional upon the occurrence or nonoccurrence of an act or event. (See, e.g., Civ. Code, § 1434 et seq.; Rest.2d Contracts, § 224; 3A Corbin, Contracts (1960) § 631, p. 21; 1 Witkin, Summary of Cal. Law (9th ed. 1987) Contracts, § 722, p. 654.) Thus, a condition precedent is either an act of a party that must be performed or an uncertain event that must happen before the contractual right accrues or the contractual duty arises. (Civ. Code, § 1436; 1 Witkin, Summary of Cal. Law supra, Contracts, § 722, p. 654.)
(1b) When, as here, the parties have agreed that a demand for arbitration must be made within a certain time, that demand is a condition precedent that must be performed before the contractual duty to submit the dispute to arbitration arises. (3b) The nonoccurrence of a condition precedent may be excused for a number of legally recognized reasons. But when a party has failed to fulfill a condition that was within its power to perform, it is not an excuse that the party did not thereby intend to surrender any rights under the agreement. (See 5 Williston, Contracts (3d ed. 1961) § 676, pp. 219-223.) A contrary conclusion would undermine the law of contracts by vesting in one contracting party the power to unilaterally convert the other contracting party’s conditional obligation into an independent, unconditional obligation notwithstanding the terms of the agreement. (1c) Thus, it is inconsistent with the law governing private arbitration agreements to assert, as plaintiffs do here, that the failure to satisfy the contractual requirement of making a timely demand for arbitration has no effect absent an intent to abandon submission of the dispute to arbitration.
Mellon Bank, N.A. v. Aetna Business Credit, 619 F.2d 1001 (3d Cir. 1980)
The generally accepted rule is that the burden of proof in regard to a condition precedent is on the party alleging the breach of the conditional promise. Standard Alliance Industries v. Black Clawson Co., 587 F.2d 813, 823 (6th Cir. 1978), cert. denied, 441 U.S. 923, 99 S.Ct. 2032, 60 L.Ed.2d 396 (1979); Ziman v. Employers Fire Insurance Co., 493 F.2d 196, 199 (2d Cir. 1974); Aetna Casualty and Surety Co. v. Harris, 218 Va. 571, 239 S.E.2d 84, 88 (1977); Allis Chalmers Manufacturing Co. v. Malan Construction Corp., 30 N.Y.2d 225, 331 N.Y.S.2d 636, 282 N.E.2d 600, 602 n. 5 (1972); Israel W. Berthiaume’s Case, 328 Mass. 186, 102 N.E.2d 412, 414 (1951); 3A Corbin, Contracts §§ 749-751; 5 Williston, Contracts § 674. The few Pennsylvania cases dealing with the burden of proving a condition precedent also suggest that the burden of proof to establish the condition is on the party alleging the breach. Dauphin Deposit Trust Co. v. World Mutual Health and Accident Insurance Co., 206 Pa. Super. 406, 213 A.2d 116
(1965); Jennison v. Aacher, 201 Pa. Super. 583, 193 A.2d 769, 772 (1963); Bossler v. Poroner, 29 Pa.Dist. 421, 12 Berks 39 (C.P. Berks County 1919).
 Therefore, the district court was in error when it placed on Aetna the burden of proving the insolvency of the borrowers as a defense to the action. Mellon had the burden of showing that the borrowers were solvent as a condition precedent to recovery for breach of Aetna’s promise.