Definition
An accomplice is a person who knowingly, voluntarily, and with common intent participates in the commission of a crime alongside a principal offender. The term is broad: it encompasses those who directly aid or assist in carrying out the offense, as well as those whose involvement is more attenuated but still deliberate and connected to the criminal act.
In modern criminal law, the concept of accomplice liability operates as a theory of culpability — meaning an accomplice can be held criminally responsible for the acts of the principal to the same degree as if the accomplice had committed the offense directly. This distinguishes the concept from mere presence or passive awareness.
Common Language
Modern common usage (Wiktionary): "An associate in the commission of a crime; a participator in an offense, whether a principal or an accessory."
Historical common usage (Webster's 1913): "An associate in the commission of a crime; a participator in an offense, whether a principal or an accessory." Also noted as a cooperator more broadly.
The gap between common and legal meaning here is not definitional but structural. In ordinary English, "accomplice" is used loosely to describe anyone involved in wrongdoing alongside another person. In legal usage, the term carries specific doctrinal weight: it triggers distinct rules about corroboration of testimony, jury instructions, and the extent of criminal liability that attach to the accomplice's conduct. A lay reader using "accomplice" informally may not appreciate that calling someone an accomplice in a legal proceeding invokes an entire framework governing what must be proven and what consequences follow.
Common Confusion
Accomplice is frequently conflated with accessory, and the two terms have overlapping but distinct meanings. Historically, the distinction turned on presence: a principal was present at the crime; an accessory was not. An accomplice could be either. Modern statutes in many jurisdictions have largely collapsed this distinction, but historical sources preserve it carefully, and the difference matters when reading older cases and treatises. Additionally, accomplice should not be confused with co-conspirator, which requires proof of an agreement to commit a crime — a separate and not always overlapping theory of liability.
Why It Matters in Research
The most significant research trap with accomplice is the shifting relationship between this term and its historical companions — accessory, abettor, principal in the second degree — across time and jurisdiction. Pre-twentieth-century sources, including Blackstone's commentaries and early American treatises, used a formal taxonomy: principal in the first degree, principal in the second degree, accessory before the fact, accessory after the fact. The word accomplice in those sources often functions as an informal umbrella term rather than a term of art, as Black's first edition confirms by noting it "includes all the participes criminis, whether considered in strict legal propriety as principals or as accessaries."
Researchers reading nineteenth-century cases should be careful not to assume that "accomplice" there carries the same doctrinal precision it carries in a modern statute or jury instruction. When a historical court calls a defendant an accomplice, it may be using the word descriptively rather than in a way that tracks the formal categories the same court used elsewhere.
A second research issue concerns accomplice testimony rules. Many jurisdictions, historically and today, require that a defendant cannot be convicted on the uncorroborated testimony of an accomplice. This rule generates a substantial body of case law on who qualifies as an accomplice for corroboration purposes — a question the dictionary definition alone does not answer. Researchers investigating conviction or acquittal in older cases should check whether the accomplice testimony rule was in play and how the particular court defined accomplice for that purpose.
Finally, modern federal law and many state statutes have replaced the common law taxonomy almost entirely with aiding and abetting statutes, which absorb much of what accomplice liability covered. Researchers moving between historical and modern sources need to track this legislative displacement carefully.
Historical Dictionary Support
The historical sources are largely in agreement on the core meaning. Black's first edition, Burrill, and Anderson all track the same formulation: one joined with another, concerned in a felony, who cooperates, aids, or assists. The phrasing echoes Russell on Crimes, reflecting the shared common law foundation these dictionaries drew from.
Rapalje & Lawrence introduces a meaningful divergence worth noting: they define accomplice as one who participates "other than as principal," which would exclude principals in the first degree from the term entirely. This is the narrower, more technically precise usage. Black's second edition, by contrast, defines accomplice as one who unites with the principal — suggesting the principal and the accomplice are distinct persons but not excluding the possibility that both are principals under the formal taxonomy.
The Anderson's Dictionary entry retrieved for this term appears to be a misfile — the text provided concerns accident insurance policy language and has no bearing on the accomplice entry. Researchers relying on Anderson's for this term should verify the source independently.
None of the historical dictionaries address accomplice testimony rules or the modern statutory treatment in aiding and abetting frameworks, which is where much of the contemporary doctrinal action occurs.
Jurisdictional Note
Federal law and most states have codified accomplice liability through aiding and abetting statutes rather than retaining the common law accomplice framework explicitly. Some states retain corroboration requirements for accomplice testimony; others do not. Researchers working on specific jurisdictions should confirm whether the common law accomplice taxonomy still operates or has been superseded by statute.
Encyclopedia Cross-Reference
Criminal Law — Accomplice Liability and Aiding and Abetting (The Law Mind Criminal Law Encyclopedia)