A number of areas of law have, of necessity, hypothetical persons whose purpose is to provide a benchmark against which particular conduct is measured. In copyright infringement analysis, there is the ordinary observer (or listener). The ordinary observer is the benchmark against which the presence or absence of substantial similarity is determined. The origins of the ordinary observer test may lie in an 1822 English decision, West v. Francis, 5 B&A 743, quoted by White-Smith Publishing Co. v. Apollo Co., 209 U.S. 1, 17 (1908): "A copy is that which comes so near to the original as to give every person seeing it the idea created by the original." "Every person" couldn't have meant literally every person, but presumably referred to a hypothetical person. By the way, unlike trademark infringement, in copyright infringement cases, survey evidence is not permitted.
In Arnstein v. Porter, 154 F.2d 464, 472-473 (2d Cir. 1946), Judge Frank offered a rare rationale for the ordinary listener test:
"Whether (if he copied) defendant unlawfully appropriated presents, too, an issue of fact. The proper criterion on that issue is not an analytic or other comparison of the respective musical compositions as they appear on paper or in the judgment of trained musicians. The plaintiff's legally protected interest is not, as such, his reputation as a musician but his interest in the potential financial returns from his compositions which derive from the lay public's approbation of his efforts. The question, therefore, is whether defendant took from plaintiff's works so much of what is pleasing to the ears of lay listeners, who comprise the audience for whom such popular music is composed, that defendant wrongfully appropriated something which belongs to the plaintiff."
In other words, the inquiry is whether defendant has captured some of plaintiff's market, as determined by those who comprise the market. This is not the same as the fourth fair use factor, but instead is a way of determining the relevant benchmark. But the market may not always be the lay public, as in Arnstein; it may be more specialized. In that case, the ordinary observer test gives way to a more specialized observer. This is seen in Dawson v. Hinshaw, 905 F.2d 731 (4th Cir. 1990), where plaintiff's gospel music arrangements were sold only in sheet music form to choral directors. Those choral directors were, therefore, the relevant market. In other cases, the market might be children, deemed to be a "less" discerning audience.
A very recent look at the ordinary listener test is Johnson v. Gordon, 2005 U.S. App. LEXIS 9902, 74 USPQ2d 1705 (1st Cir. May 31, 2005), a music infringement case. While in most respects Johnson is straightforward, one aspect is disturbing, its reliance on "experts" for the ultimate question of substantial similarity. That was error. Experts, if permitted at all in non-computer program infringement cases (and Learned Hand thought they should be banned altogether, as do some sitting appellate judges I know) should be limited to testifying about whether defendant copied or not. By letting experts opine about substantial similarity not only are those experts testifying about the ultimate fact question, they are subverting the entire basis for the ordinary observer test.
[On Monday the "more discerning" observer test].