I should note beforehand that much of my legal "knowledge" is based off of TV shows and movies so some of my assumptions might be off.

When you take the stand at a trial, you promise to tell "the truth, the whole truth, and nothing but the truth." But it seems like most witnesses do not tell the whole truth, at least right away.

For example, lawyers often give certain lines of questioning to develop an argument. From what I understand, witnesses are encouraged to simply answer the questions asked and not say much more.

But often there is a lot more nuance and a lot more additional evidence that could paint the story in a different light. If you are simply responding to a lawyer's line of questioning, and the lawyer's line of questioning is not complete, then your responses are not telling the whole truth. And because lawyers are usually representing one side or the other, they rarely give a complete line of questioning and only ask the questions that support their side of the case.

Does this mean that most witnesses are not telling the whole truth?


First off, the concept of "the whole truth" is legally undefined. It cannot possibly mean "everything that you know that is connected to this question", since otherwise a witness would be required to drone on and on for hours. Second, there is no way to determine what percentage of witnesses are not "telling the whole truth". We can be fairly certain that when a guilty accused takes the stand, there is a good chance that he is not telling the whole truth, and the oath does not compel you to testify against yourself. Even if there was some clear legal definition of "the whole truth", there is typically no way to know what the actual facts are, to know if a witness failed to say something that was part of "the whole truth".

The promise part of the oath is irrelevant, that is, the requirement is not to "keep your promise", it is to not perjure yourself. Every jurisdiction in the US has a statute that makes it a crime to commit perjury. At the federal level, the law is 18 USC 1621, which applies to anyone who has "taken an oath" promising to testify truly, and punishes the witness if he "willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true".

The landmark ruling Bronston v. US, 409 US 352 clarified the obligation of witnesses vs. the duty of interrogators, when it comes to not providing information desired by the interrogator. The court ruled that the perjury statutes does not apply to a

witness's answer that is literally true, but unresponsive, even assuming the witness intends to mislead his questioner by the answer, and even assuming the answer is arguably "false by negative implication." A perjury prosecution is not, in our adversary system, the primary safeguard against errant testimony; given the incongruity of an unresponsive answer, it is the questioner's burden to frame his interrogation acutely to elicit the precise information he seeks.

This was a classical "not the whole truth" case. The exchange was as follows, where the accused was testifying in bankruptcy proceedings:

Q. Do you have any bank accounts in Swiss banks, Mr. Bronston?

A. No, sir.

Q. Have you ever?

A. The company had an account there for about six months, in Zurich.

The fact is that Bronston used to have a personal account in a Swiss Bank, which he did not reveal. His answer could be considered misleading because he only answered part of the question, as it pertained to the company (but not him personally). The crux of the court's ruling is that it is the responsibility of the attorney conducting the interrogation to notice that he did not answer the question asked, and to insist on a response that also covers personal accounts. This established the "literal truth" doctrine for perjury conviction: if what you say is literally true, the testimony is not perjurous. As a later court (DeZarn) commented,

because a nonresponsive answer, by its nature, requires speculation by the fact-finder as to what the answer “implies”, there cannot be a finding beyond a reasonable doubt that the answer is untruthful.

Clinton successfully relied on this defense with respect to certain of his literally-true testimony.

One tweak on this is US v. DeZarn, 157 F3d 1042, where a literal-truth defense was set forth but rejected by the court. The accused was asked about a party that was allegedly a fundraising event. His testimony was that it wasn't a fundraising event for the governor (in fact it was), and his defense came down to the fact that the prosecutor asked about a party in 1991, had earlier referred to it as a "Preakness Party" (which the governor had held previously), and asked about fundraising "at that activity". DeZarn's claim was that he thought the prosecutor was asking about a party in 1990 (which was a "Preakness Party", with no fundraising). The prosecutor was in error in previously calling it a "Preakness Party", but was correct in identifying that there was a party (with fundraising) at the governor's house, in 1991 time.

The wording of DeZarn's testimony was, simply "I don't know... No... No": these are responses that have no literal truth value taken on their own, and can be judged only in relation to what question was asked (whereas Bronston's testimony was literally true on its own). DeZarn's conviction was upheld because he could not have been confused about which party was being referred to, and what the actual question was; moreover, in saying just "No", he gave no sign that his response was a partial answer to the question.

The DeZarn court did not clarify matters, leaving it at the conclusion that

a perjury inquiry which focuses only upon the precision of the question and ignores what the Defendant knew about the subject matter of the question at the time it was asked, misses the very point of perjury:  that is, the Defendant's intent to testify falsely and, thereby, mislead his interrogators.

This does not clearly distinguish DeZarn from Bronston, but that could be remedied by a more precise theory of the linguistic relationship between the question(s) asked and the literal answer – Bronston said enough that a reasonable person could detect that only part of the question was answered, whereas the testimony "No" gives no overt sign that the testifier had privately re-written the question to be something like "Was there fundraising at a Preakness Party in 1991", as opposed to "at that activity". The court relied on a subjective "sniff test" for distinguishing responsive from non-responsive testimony, so I would say that they simply did not draw the bright lines that could have been drawn (which would be based on better distinguishing "implies" versus "asserts").

  • Let me give an example of what I'm thinking. Imagine there exists a rare disease that 1 in 1,000 people have, and a test for the disease that is 99% accurate. Bayesian analysis shows that if the test results in a positive, there is still a 90% chance you don't have the disease. If a prosecutor asked if someone getting positive on this test means they had the disease, and you responded "The test is 99% accurate," I would consider that not the whole truth, at least according to the colloquial usage of the term. But I suppose "the whole truth" is taken very narrowly based on what you said.
    – user35734
    Jul 19 '17 at 3:47
  • 2
    This is exactly where the attorney is supposed to probe deeper and rephrase the question, to reveal whatever unspoken details there are. The prosecutor would need to understand the underlying science, which is why both sides hire specialists.
    – user6726
    Jul 19 '17 at 4:09
  • I was hoping there was some responsibility on the person taking the stand to say more than just strictly answering the question. But I suppose as long as you have a competent lawyer that shouldn't be an issue.
    – user35734
    Jul 20 '17 at 4:16
  • @user35734: witnesses taking the stand will vary from minor children to allegedly senile adults (competency hearings for example), and they are people with agendas of their own. Truth can be demanded and enforced, wisdom and seeking justice, not so much.
    – jmoreno
    Apr 3 at 0:30

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