See also: CONDITIONAL ADMISSION.

1.  Generally

Questions of conditional relevancy are those which depend solely upon the existence of a particular preliminary fact rather than upon the application of the protective policies of an exclusionary rule.{footnote}United States v. James, 590 F.2d 575, 579 (5th Cir.), cert. denied, 442 U.S. 917 (1979).
Burlington Northern Railroad Company v. Hood, 802 P.2d 458, 466 (Colo. 1990) (whether witness has the requisite personal knowledge to testify under Colo. R. Evid. 602 is matter of conditional relevancy and is for the jury to resolve).
1 J. Weinstein & M. Berger, Weinstein’s Evidence & 104[02], at 104-20 (1990); E. Morgan, Basic Problems of Evidence 45-46 (4th ed. 1963).{/footnote}  They are governed by FRE 104(b) and its state counterparts, which provide:

When the relevancy of evidence depends upon the fulfillment of a condition of fact, the court shall admit it upon, or subject to, the introduction of evidence sufficient to support a finding of the fulfillment of the condition.

Such questions are ultimately for the trier of fact to determine.{footnote}FRE 104(b), Advisory Committee’s Note.
Burlington Northern Railroad Company v. Hood, 802 P.2d 458, 466 (Colo. 1990).{/footnote}  The trial court merely makes a preliminary determination whether sufficient foundation exists to support a finding that the condition has been fulfilled.{footnote}FRE 104(b)
Burlington Northern Railroad Company v. Hood, 802 P.2d 458, 466 (Colo. 1990).{/footnote} The test has been stated as whether the jury could reasonably find by a preponderance of the evidence that the conditional fact has been established.{footnote}Huddleston v. United States, 485 U.S. 681, 690, 99 L. Ed. 2d 771, 108 S. Ct. 1496 (1988); United States v. 478.34 Acres of Land, Tract No. 400, 578 F.2d 156, 159-160 (6th Cir. 1978); 1 Weinstein’s Evidence para. 104[09], at 104-78 to 79.
Burlington Northern Railroad Company v. Hood, 802 P.2d 458, 466 (Colo. 1990).{/footnote}

2.  “Connecting Up”

Evidence may be admitted subject to "connecting up"–i.e., proof of a fact necessary to make the evidence introduced relevant.{footnote}FRE 104(b). 
See, e.g., In re TMI Litigation Cases Consol. II, 922 F. Supp. 1038 (M.D. Pa. 1996) (expert medical testimony assuming certain extent of exposure to radiation admissible subject to proof actual extent of exposure).{/footnote}  The admission of the evidence is considered conditional because the evidence will be stricken if the facts necessary to make it relevant are not yet proved.   Where no showing of relevance is ever made, the opposing party must make a timely objection or the objection is deemed waived.{footnote}United States v. Gilbreath, 445 F.2d 810, 810-11 (10th Cir.) (per curiam), cert. denied, 404 U.S. 958 (1971); Anglo Cal. Nat’l Bank v. Lazard, 106 F.2d 693, 705-06 (9th Cir.), cert. denied, 308 U.S. 624 (1939); Franano v. United States, 277 F.2d 511, 516 (8th Cir.), cert. denied, 364 U.S. 828, reh’g denied, 364 U.S. 906 (1960).{/footnote}