In a legal sense, the term conjecture refers to guesswork, meaning it is a supposition based on theory or opinion, without substantial evidence. Conjectures are often based on the way a situation appears, rather than on solid proof. For instance, the media often makes conjectures about the state of celebrities’ marriages based on rumor and photos submitted by unsubstantiated sources. To explore this concept, consider the following conjecture definition.

Definition of Conjecture


  1. The expression of a theory, or of an opinion, based on speculation, without substantial proof.
  2. A conclusion reached by guesswork.


1350-1400       Middle English

What is Conjecture

Conjecture is a theory based on evidence with only a slight degree of credibility. It is an idea of fact, or potential cause or occurrence, as suggested by another fact, which is too feeble to prove the idea.  A conjecture is even less substantial than a hypothesis, which is generally based on well-accepted facts. For instance, it is well known that moisture evaporates into the atmosphere over time. A hypothesis could be made, then, that the water level in a manmade pond could become lower and lower, eventually causing problems for the fish in the pond.

By contrast, a conjecture relies on facts that are likely to be true, based on other facts, though they may not be true. Someone engaging in conjecture may ask that a certain fact be considered true, based on related facts, for the purposes of making a point, or coming to a decision.

Example of Conjecture

TrueBlue marketing company is looking to hire a new ad agent. Nick’s resume boasts a number of accomplishments, as well as two CLIO awards for advertising. As nobody in the company has actually seen any of Nick’s work, nor has any actual knowledge that the statements in his resume are true, there is no actual proof that he is good at his job. The company, based on conjecture resulting from the statements made in his resume, offers Nick a job.

Substantial Evidence

In differentiating between conjecture and reasonable inference, the term substantial evidence is often used. Substantial evidence is enough to lead a reasonable person to a specific conclusion. The U.S. Supreme Court has defined substantial evidence as “more than a mere scintilla,” and “… such relevant evidence as a reasonable mind might accept as adequate to support a conclusion.”

Substantial evidence is not the same thing as any evidence. In order for evidence to be credible enough to support a verdict, it must provide adequate proof of each of the essential elements of the case. Still, inferences may be made, as long as they are the result of logic and sound reasoning, based on the available evidence. An inference based on conjecture cannot be used to make a legal determination.

In the scientific field, substantial evidence results from controlled trials, investigations, and clinical studies, carried out by qualified experts.

Conjecture Example of a Trial Objection

Proving one’s case at either a criminal or civil trial is done by presenting evidence, questioning witnesses, making speeches, and issuing objections to information the opposing side attempts to present. There are certain specific rules that must be adhered to in courtroom matters, including trials. It is important for those who practice law have a very good understanding of, not only the laws relating to the specific case, but of the rules and procedures of the court. Failure to adhere to the rules may result in an objection by the opposing party, which may lead to serious consequences for the case.

Objecting in the courtroom is not a free-for-all in which opposing parties constantly interrupt the proceedings to tell the judge they don’t like what the other party’s witness is saying, or that they don’t think it’s fair for certain evidence to be shown to the jury. If that were the case, the judicial system would have collapsed long ago under endless arguments. Timely and skilled trial objections, however, help keep the trial from devolving into courtroom mayhem.

There are certain types of objections that are commonly made in court, each of which addresses a breach of a rule, procedure, or law. Conjecture, also referred to as “speculation,” addresses the issue of suggesting or adopting a theory based on circumstances surrounding facts that don’t actually prove the theory. The primary types of trial objection include:

  • Speculation (conjecture) – an objection lodged when a question invites a witness to answer based on conjecture, or a guess. Example of a question inviting conjecture: “Do you think that made Mr. Smith angry enough to kill his wife?”
  • Leading Question – an objection made when the opposing party phrases a question in such a way as to suggest the desired answer. Leading questions are allowable during cross-examination. Example of a leading question: “And Mr. Brown darted across the intersection without stopping, correct?”
  • Hearsay – an objection lodged when a witness is invited to offer a statement made out of court to prove the truth of matter in court. It also applies when a witness quotes what someone else said, when being questioned. Example of hearsay testimony: “When Becky and I were talking over drinks, she said her husband was having an affair.”
  • Irrelevant – an objection made when evidence or testimony has nothing to do with the case, but which could damage one party’s position.

Examples of Conjecture During Trial

In order for a witness to testify about something, he must have personal knowledge of that fact. This may come from being present to witness or hear something, it may be something he is educated about, or he may be otherwise directly involved in some way. Witness testimony regarding anything about which he does not have first-hand knowledge is considered speculation, or conjecture, and is not allowed.

There are basically two ways conjecture becomes an issue at trial: (1) an attorney asks a witness a question which requires the witness to speculate, or guess at the answer; (2) a witness offers conjecture, or speculation, in answer to a legitimately phrased question.

Example of conjecture encouraged by the phrasing of a question:

“Did the neighbor’s statement make your husband angry?”

In this case, the question required the witness to testify as to how her husband felt after a confrontation with the neighbor.

Example of conjecture offered freely:

Question: Were you present during the conversation between your husband and his boss?

Answer: “Yes, and Helen had lied to his boss, saying John was making advances toward her.”

In this example of conjecture, the question was phrased properly, but the witness added her guess about what had happened, based on what she was told Helen said to someone else.

Objections based on conjecture at trial are most often made based on the way a question is asked, leading the witness to a particular answer.

Conjecture and Objections in the O.J. Simpson Trial

In 1994, former football star O.J. Simpson was arrested and charged with the brutal murders of his ex-wife, Nichole Brown Simpson, and her friend, Ronald Goldman. The trial, which began on January 24, 1995, was the first in U.S. history to be televised from start to finish and it was a long, drawn-out process that lasted more than seven months. The lengthy trial was due to the nature of the crime, combined with the fact that Mr. Simpson was a long-held sports hero, which lent to a pattern of near-constant interruptions for objections and side-bar conferences.

In an attempt to create reasonable doubt about Simpson’s involvement in the murders, the defense team attempted to suggest that drug dealers had sent “hit men” after Nichole’s friend, Faye Resnick, who had failed to pay for her drugs, and that Nichole and Ronald were the victims of their mistaken identity. The prosecution objected, calling the theory far-fetched conjecture. After hearing the prosecution’s objection, the judge ruled that Simpson’s defense team had not shown sufficient evidence that such a scenario was even possible. In barring any testimony about Resnick’s drug use, Judge Ito emphasized that he found what little evidence the defense had offered to be conjecture of the highest order.

Conjecture in the Casey Anthony Trial

In July, 2008, 2-year old Caylee Marie Anthony was reported missing from her home by her grandparents. The grandparents were concerned because that had not seen Caylee for more than 30 days, and they told police they suspected their daughter Casey, Caylee’s mother, had done something to her. In fact, the grandparents reported that their daughter’s car had the odor of a dead body.

Even before the toddler’s remains were found on December 11, 2008, Casey Anthony was charged with first degree murder, aggravated manslaughter of a child, aggravated child abuse, and four counts of providing false information to police. Prosecutors asked for the death penalty.

During the trial, which began May 24, 2011, a great deal of evidence was presented, supporting the prosecution’s theory that Casey had murdered her little girl, and dumped her body in a garbage bag. Such evidence included hair samples in Casey’s car that was microscopically similar to hairs taken from Caylee’s hair brush, and which showed signs of decomposition, a strong odor of human decomposition in the car, chemical compounds consistent with the presence of a decomposing body found in Casey’s car, and the discovery of Google searches on Casey’s home computer for instructions in making chloroform, neck-breaking, and suffocation.

Casey had claimed, among other inconsistent stories, that her daughter had been kidnapped by a nanny, later determined to be a fictional person. The defense team put forward the notion that the little girl had accidentally drowned in the family pool, and Casey simply didn’t know what to do with the body.

Although conjecture and speculation have no place in a process that requires proof of wrongdoing beyond a reasonable doubt, Assistant State Attorney Jeff Ashton encouraged the jury to speculate about how the murder was committed, and told them they were free to use conjecture in reaching a verdict. Ashton told the jury, “You can reconstruct these events any way you want.” He further incited reliance on conjecture by adding that, regardless of each juror’s theory of how little Caylee died, if it involved any intentional act that resulted in harm to the child, it amounted to felony murder.

By contrast, defense attorney Jose Baez became concerned that emotional turmoil the case stirred up for the entire nation, would play against Casey with the jury. At the end of the nearly two-month trial, Baez reminded the jury that Casey’s guilt had to be proven to the exclusion of every reasonable doubt. He told the jury members not to guess, and not to engage in conjecture. He insisted, “There should be no mystery before you now. If you have questions, then it was not proved.”

Related Legal Terms and Issues

  • Inference – A conclusion reached on the basis of evidence and reasoning.
  • Beyond a Reasonable Doubt – The standard of proof required in a criminal trial: that no other logical explanation exists, given the facts presented, that the accused committed the crime.
  • Side Bar – A conference between the judge and lawyers, held out of earshot of the jury and spectators.
  • Verdict – The decision of the jury after the trial of a case.
  • Witness – An individual who can provide a firsthand account of something heard, seen, or experienced.

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