Although the lesser included offense doctrine developed at common law to assist the prosecution in cases where the evidence failed to establish some element of the offense originally charged, it is now beyond dispute that the defendant is entitled to an instruction on a lesser included offense if the evidence would permit a jury rationally to find him guilty of the lesser offense and acquit him of the greater.
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Moreover, it is no answer to petitioner's demand for a jury instruction on a lesser offense to argue that a defendant may be better off without such an instruction. True, if the prosecution has not established beyond a reasonable doubt every element of the offense charged, and if no lesser offense instruction is offered, the jury must, as a theoretical matter, return a verdict of acquittal. But a defendant is entitled to a lesser offense instruction -- in this context or any other -- precisely because he should not be exposed to the substantial risk that the jury's practice will diverge from theory. Where one of the elements of the offense charged remains in doubt, but the defendant is plainly guilty of some offense, the jury is likely to resolve its doubts in favor of conviction. In the case before us, for example, an intent to commit serious bodily injury is a necessary element of the crime with which petitioner was charged, but not of the crime of simple assault. Since the nature of petitioner's intent was very much in dispute at trial, the jury could rationally have convicted him of simple assault if that option had been presented. But the jury was presented with only two options: convicting the defendant of assault with intent to commit great bodily injury or acquitting him outright. We cannot say that the availability of a third option -- convicting the defendant of simple assault -- could not have resulted in a different verdict. Indeed, while we have never explicitly held that the Due Process Clause of the Fifth Amendment guarantees the right of a defendant to have the jury instructed on a lesser included offense, it is nevertheless clear that a construction of the Major Crimes Act to preclude such an instruction would raise difficult constitutional questions."
