In Boyde v. California (1990) 494 U.S. 370, the high court surveyed its previously disparate treatment of erroneous jury instructions. (Id. at pp. 378-380.) First, the court distinguished those cases wherein "a jury is clearly instructed by the court that it may convict a defendant on an impermissible legal theory, as well as on a proper theory or theories. Although it is possible that the guilty verdict may have had a proper basis, 'it is equally likely that the verdict ... rested on an unconstitutional ground,' , and we have declined to choose between two such likely possibilities." (Id. at p. 380.) By contrast, the court observed that in the case before it, "we are presented with a single jury instruction. The instruction is not concededly erroneous ... . The claim is that the instruction is ambiguous and therefore subject to an erroneous interpretation. We think the proper inquiry in such a case is whether there is a reasonable likelihood that the jury has applied the challenged instruction in a way that prevents the consideration of constitutionally relevant evidence." (Ibid.) The court in Boyde thereby limited the reasonable likelihood standard to cases involving a single ambiguous instruction.