“Why presuming innocence has nothing to do with assigning low prior probabilities to the proposition that defendant didn’t commit the crime”

by Professor Larry Laudan

Philosopher of Science*

Several of the comments to the July 17 post about the presumption of innocence suppose that jurors are asked to believe, at the outset of a trial, that the defendant did not commit the crime and that they can legitimately convict him if and only if they are eventually persuaded that it is highly likely (pursuant to the prevailing standard of proof) that he did in fact commit it. Failing that, they must find him not guilty. Many contributors here are conjecturing how confident jurors should be at the outset about defendant’s material innocence.

That is a natural enough Bayesian way of formulating the issue but I think it drastically misstates what the presumption of innocence amounts to. In my view, the presumption is not (or at least should not be) an instruction about whether jurors believe defendant did or did not commit the crime. It is, rather, an instruction about their probative attitudes.

There are three reasons for thinking this:

a). asking a juror to begin a trial believing that defendant did not commit a crime requires a doxastic act that is probably outside the jurors’ control. It would involve asking jurors to strongly believe an empirical assertion for which they have no evidence whatsoever. It is wholly unclear that any of us has the ability to talk ourselves into resolutely believing x if we have no empirical grounds for asserting x. By contrast, asking juries to believe that they have seen as yet no proof of defendant’s guilt is an easy belief to acquiesce in since it is obviously true.

b). asking jurors to believe that defendant did not commit the crime seems a rather strange and gratuitous request to make since at no point in the trial will jurors be asked to make a judgment whether defendant is materially innocent. The key decision they must make at the end of the trial does not require a determination of factual innocence. On the contrary, jurors must make a probative judgment: has it been proved beyond a reasonable doubt that defendant committed the crime? If they believe that the proof standard has been satisfied, they issue a verdict of guilty. If not, they acquit him. It is crucial to grasp that an acquittal entails nothing about whether defendant committed the crime, What it focuses on is how strong or weak is the proof that he did so. Because their verdict decision is entirely a question about whether guilt has been proven or not, the guilt-not-proven verdict leaves wholly unresolved the issue whether the defendant did or did not commit the crime. Boastful claims to the press from defense attorneys about how their newly acquitted clients have been ‘exonerated’ or ‘vindicated’ are patently misleading. What they should be proclaiming on the courthouse steps is something like: “There’s at least a 5-10% chance that my client didn’t commit the crime.” (Except in Scotland, ‘innocence’ simply does not figure among the verdict options open to Anglo-Saxon jurors.)

c). Legal jurisprudence itself makes clear that the presumption of innocence must be glossed in probatory terms. Consider this model federal jury instruction:

The law presumes defendant to be innocent of all the charges against him. I therefore instruct you that the defendant is to be presumed by you to be innocent throughout your deliberations until such time, if ever, you as a jury are satisfied that the government has proven him guilty beyond a reasonable doubt.” US v. Walker (1988)

Bayesians will of course be understandably appalled at the suggestion here that, as the jury comes to see and consider more and more evidence, they must continue assuming that defendant did not commit the crime until they make a quantum leap and suddenly decide that his guilt has been proven to a very high standard. This instruction makes sense if and only if we suppose that the court is not referring to belief in the likelihood of material innocence (which will presumably gradually decline with the accumulation of more and more inculpatory evidence) but rather to a belief that guilt has been proved.

As I see it, the presumption of innocence is nothing more than an instruction to jurors to avoid factoring into their calculations the fact that he is on trial because some people in the legal system believe him to be guilty. Such an instruction may be reasonable or not (after all, roughly 80% of those who go to trial are convicted and, given what we know about false conviction rates, that clearly means that the majority of defendants are guilty). But I’m quite prepared to have jurors urged to ignore what they know about conviction rates at trial and simply go into a trial acknowledging that, to date, they have seen no proof of defendant’s culpability.

Larry Laudan

*Currently a Professor of Philosophy & Law, The University of Texas School of Law

Among Laudan’s books:

1977. Progress and its Problems: Towards a Theory of Scientific Growth

1981. Science and Hypothesis

1984. Science and Values

1990. Science and Relativism: Dialogues on the Philosophy of Science

1996. Beyond Positivism and Relativism

2006. Truth, Error and Criminal Law: An Essay in Legal Epistemology