Page:United States Reports, Volume 545.djvu/1010

 , J., concurring U.S., at 441–442. Compare Cable/Home Communication Corp., supra, at 837–850 (developer liable for advertising television signal descrambler), with Vault Corp., supra, at 262 (primary use infringing but a substantial noninfringing use).

Sony’s rule is forward looking. It does not conﬁne its scope to a static snapshot of a product’s current uses (thereby threatening technologies that have undeveloped future markets). Rather, as the VCR example makes clear, a product’s market can evolve dramatically over time. And Sony—by referring to a capacity for substantial noninfringing uses—recognizes that fact. Sony’s word “capable” refers to a plausible, not simply a theoretical, likelihood that such uses will come to pass, and that fact anchors Sony in practical reality. Cf. Aimster, 334 F.3d, at 651.

Sony’s rule is mindful of the limitations facing judges where matters of technology are concerned. Judges have no specialized technical ability to answer questions about present or future technological feasibilility or commercial viability where technology professionals, engineers, and venture capitalists themselves may radically disagree and where answers may differ depending upon whether one focuses upon the time of product development or the time of distribution. Consider, for example, the question whether devices can be added to Grokster’s software that will ﬁlter out infringing ﬁles. MGM tells us this is easy enough to do, as do several amici that produce and sell the filtering technology. See, e.g., Brief for Motion Picture Studio and Record ing Company Petitioners 11; Brief for Audible Magic Corp. et al. as Amici Curiae 3–10. Grokster says it is not at all easy to do, and not an efﬁcient solution in any event, and several apparently disinterested computer science professors agree. See Brief for Respondents 31; Brief for Computer Science Professor Harold Abelson et al. as Amici Curiae 6–10, 14–18. Which account should a judge credit? Sony says that the judge will not necessarily have to decide.