Concept
Why Impossibility Fails
Factual Impossibility
Why Impossibility Fails
Two separate supports hold up the common-law rule, and each answers a different objection a defendant might raise. The first concerns timing. The gist of conspiracy is the agreement itself, so the offense is punishable even when its purpose is never achieved, and a later discovery that the objective was out of reach arrives after the crime already exists.1 The second concerns the harm the offense is aimed at. A group organized for criminal purposes is dangerous apart from the danger of attaining the particular objective, so a plan that could never have worked has still produced the thing conspiracy exists to reach.2
Keeping the two reasons apart helps because they meet different versions of the impossibility argument. A defendant who says nothing came of the plan is answered by the first reason, since the prosecution never had to prove that anything came of it. A defendant who says the plan was harmless because it could never have succeeded is answered by the second, since the harm conspiracy punishes is the continuing danger of the group, and a hidden flaw in one plan does not remove that danger. Together the reasons also explain why conspiracy parts company with attempt. Impossibility has arisen far more often in attempt law, where the offense is defined by how near the defendant's conduct came to the completed crime, and a plan that could never be completed can therefore matter.3 Conspiracy is defined by the agreement and the group danger, so the same argument finds little to work on. The first reason, the agreement as the gist of the offense, comes first, because its history shows how conspiracy came to be punishable without any completed harm.
Agreement as the Gist
The first support for the common-law rule comes from what the crime of conspiracy actually consists of. Conspiracy requires an agreement between two or more people, which supplies the act, and an intent by those people to achieve an unlawful objective.4 The agreement counts as the act because the parties have done something real once they commit to a shared plan: each person's private intention has become a joint undertaking, which is why courts have so often called the agreement the essence, or gist, of the offense. Many jurisdictions add a requirement of an overt act, meaning a step taken in furtherance of the plan, but that requirement is usually treated as an evidentiary safeguard and not as another element. If the agreement is the crime, the offense is finished at the moment the agreement is made, and whether the plan could later be carried out is a question the prosecution never had to answer.
The law did not always work this way, and the history shows why the shift mattered. Conspiracy was unknown to the early common law and entered English law through statutes under Edward I that were aimed at abuses of criminal procedure.5 Because of that purpose, the offense was defined narrowly: only combinations to procure false indictments, bring false appeals, or maintain vexatious suits qualified. The crime was also incomplete unless the falsely accused person had actually been indicted and acquitted. Under that early version, then, whether a conspiracy existed depended on how the scheme turned out, and an agreement that never carried the victim through an indictment and an acquittal was not yet the crime.
The Court of Star Chamber broke that dependence on outcome in Poulterers' Case (1611). The defendants there had confederated to bring a false accusation against a man named Stone, but Stone was so clearly innocent that the grand jury refused to indict him.6 Following the older law, the defendants argued that without an indictment no conspiracy had occurred. The court decided otherwise, and the decision gave rise to a doctrine that survives today: the gist of conspiracy is the agreement, so the agreement is punishable even if its purpose was not achieved. The plan in that case had failed because of facts outside the defendants' control, namely Stone's evident innocence and the grand jury's response. The court held them guilty anyway, and that holding is the root of the modern statement that conspiracy does not wait on success.
The reason the law moved this way can be read off the structure of the offense. When the parties agree, the culpable mind (each person intends the unlawful objective) and the union of purpose (each is committed to the others) are both fully present. Those two ingredients are what make a criminal combination worth punishing. A grand jury's refusal to indict, an emptied safe, or a target who has already died happens after the agreement, and an event that follows a completed offense can neither add to the crime nor subtract from it. For that reason the modern rule treats it as unnecessary that the agreed objective actually be achievable, and unnecessary that anyone suffer a loss, because the crux of the crime is the agreement and not the commission of the object.7 Conspiracy shares this feature with the other inchoate offenses, attempt and incitement, each of which can be committed although the substantive offense is never consummated.8 Applied to impossibility, the idea yields the common-law rule that factual impossibility is no defense.9
The same reasoning marks where the rule stops. Because the agreement is the crime, a person who never agreed has nothing for the rule to reach, and impossibility never enters the analysis. The agreement need not be written or even spoken in so many words, since a tacit understanding can suffice and the parties' conduct can show it.10 It must still be a genuine commitment to act together.
The pair of situations differs in a single respect, the presence of a commitment, and that difference decides the result. On an exam stem, the order of questions matters. The first question is whether the parties reached an agreement with the intent to achieve an unlawful objective. Only when the answer is yes does the later failure of the plan become relevant, and then it matters only to show that the failure changes nothing. Students lose this issue by reaching for impossibility when the real problem is that no agreement was ever formed. The next section turns to the second support for the rule, the danger a criminal group poses apart from the particular plan.
Group Danger Beyond the Object
The second support for the common-law rule looks past the single plan to the people who made it. A group organized for criminal purposes is dangerous apart from the danger of reaching its particular objective, which is why a plan that could never have worked still leaves something for conspiracy law to punish.12 A group adds more than one person's intention. Each member's resolve is reinforced by the others, the work can be divided, and people who have learned to act together can redirect their effort to a new target as easily as they pursued the first. The common law captured the point in the maxim that in union there is strength, and it therefore treated the formation of a conspiracy as a distinct evil from the crime the members contemplated.13
The harm this rationale identifies has two parts, and they work differently. The first is a standing capacity: a criminal grouping is a continuing focal point for further crimes, whether related to the plan at hand or unrelated to it.14 Because that capacity belongs to the group rather than to any single scheme, the failure of one scheme leaves it untouched. The second part is diffuse. Merely knowing that criminal groupings exist makes a community less secure, so this harm is already present once the group has formed, and it does not wait for any offense to be completed.15 Together the two harms explain why the state's interest in stamping out conspiracy reaches beyond its interest in preventing any specific offense, and why an unreachable objective cures neither one.
The example gives the defendants about as favorable a set of facts as the defense could ask for, because the only object they named was unreachable from the start. Their argument treats the object offense as the only harm conspiracy addresses, and that premise is the weak point. Once the harm is located in the group, the emptied building changes which targets are available and leaves the three exactly as dangerous as they were before they learned of it.
Attempt law, where the impossibility defense first took shape, rested on a narrower purpose, and the contrast explains why the defense found a home there and not here. Courts traditionally assumed that attempt exists to deal with conduct that creates a risk of immediate harm. On that assumption, an actor whose conduct could never have come near the completed crime presented no danger of the kind attempt targets, so the older cases saw nothing to gain from intervening and treated such conduct as innocuous.16 The reasoning is sound on its own premise, since an act that could never come near harm creates no immediate risk. Conspiracy rests on a broader premise. Its charge focuses on the defendants' intent and their agreement, and it does not ask how near anyone's conduct came to the finished crime, so the impossibility of the object is far less pertinent.17 Modern attempt law has itself moved toward the conspiracy view, because it now treats attempt as a way to proceed against people who have shown their dangerousness, a showing that an unreachable object does not undo.18
Students lose this point when they carry the older attempt reasoning into a conspiracy question and argue that a plan that could never succeed is harmless. That argument has a place in attempt, where closeness to harm is the concern. In conspiracy the harm lies in the group, so the argument has no premise to rest on. Which mistakes the rule does reach is a separate question, because the vocabulary of factual and legal impossibility comes from attempt law, and the next section uses it to sort impossibility claims.