Definition
A challenge principal is a formal objection to a prospective juror (or, historically, to any person summoned to serve in a judicial capacity) that, if proved true, is conclusively sufficient to disqualify that person without any further inquiry into the state of their mind or conscience. It operates as a matter of law: once the stated ground is established, disqualification follows automatically.
The term belongs to the law of jury challenges and sits within the broader category of challenges to the polls — that is, objections directed at individual members of the jury panel, as distinguished from challenges to the array, which attack the panel as a whole.
Within challenges to the polls, the traditional division runs between:
1. Challenge principal: A challenge resting on a ground so weighty that the law presumes bias or incapacity conclusively. No discretion is left to the triers of the challenge. If the fact is found, the juror is gone.
2. Challenge to the favor (challenge propter affectum, partial form): A challenge resting on circumstances that suggest possible partiality but do not rise to the level of a principal challenge. The triers retain discretion to assess whether actual bias exists.
The classic examples of grounds supporting a challenge principal include: the juror being of alien status (historically), having a direct financial interest in the outcome, being related to one of the parties within a prohibited degree, or having already served on a prior jury in the same matter.
Common Confusion
Challenge principal is sometimes loosely conflated with challenge for cause, and in modern practice the terms are often used interchangeably or the older classification is abandoned entirely. They are not, however, identical at common law. Challenge for cause is the broader genus; challenge principal is a specific species within it, distinguished by the conclusiveness of its effect. A challenge for cause may leave something to the discretion of the triers; a challenge principal does not. Modern procedural codes have largely collapsed this distinction, replacing the common-law taxonomy with a unified "for cause" framework, which means historical sources using the term challenge principal are operating within a classificatory scheme that current rules do not preserve.
Why It Matters in Research
The primary research trap is anachronism. A researcher reading nineteenth-century treatises, English common-law reports, or early American state court opinions will encounter challenge principal as a term of art with precise technical meaning. Modern jury-selection materials, federal rules commentary, and contemporary case law will rarely use the phrase; they have absorbed the concept into the general "for cause" category without preserving the principal/favor distinction. Bridging those two bodies of material requires recognizing that what older sources call a challenge principal is what modern sources call a per se or conclusive ground for disqualification for cause.
The Lord Coke formulation — that the challenge is "principal" because it stands sufficient of itself, leaving nothing to the conscience or discretion of the triers — is the governing conceptual key. When reading historical jury-challenge doctrine, the question to ask is always: does this ground operate conclusively (principal), or does it leave something to the triers' judgment (to the favor)? That distinction controls the procedural consequences in the historical materials.
Researchers working on the history of jury impartiality doctrine, Sixth Amendment development, or comparative Anglo-American procedure will find challenge principal doctrine at the foundation. The constitutional guarantee of an impartial jury absorbed and partially displaced the common-law challenge structure, but the older categories continue to appear in historical sources, older state court decisions, and treatises through at least the late nineteenth century.
Note also that Blackstone's treatment differs slightly from Coke's. Blackstone, as Burrill records, confined the label "principal" specifically to the propter affectum (bias/partiality) branch of challenges — meaning he used "principal" to distinguish the clearer partiality grounds from the closer ones, not to describe all conclusive disqualifications across every category. Coke's usage is broader. A researcher encountering either formulation should identify which authority the source is following before drawing conclusions.
Historical Dictionary Support
Burrill's Law Dictionary is the primary shelf source for this term and provides the essential framework. Burrill traces two competing explanations for the label "principal": Coke's functional explanation (the challenge stands sufficient of itself, nothing left to triers' discretion) and Blackstone's more limited usage (confined to the propter affectum branch, where the cause assigned carries with it a presumption of partiality strong enough to be self-proving). The fragment from Burrill cuts off mid-sentence in the Blackstone explanation, but the substance is recoverable from Blackstone's Commentaries, Book III, chapter 23, and from Coke's Institutes, Co. Litt. 156b.
Neither source fully addresses how American courts adapted or abandoned the distinction. That gap is significant: American jurisdictions varied in how faithfully they preserved the English taxonomy, and by the time the Field Code reforms and later federal rules took shape, the challenge principal as a distinct doctrinal category had largely dissolved into "challenge for cause." Historical dictionaries other than Burrill give this term little or no treatment, which itself signals how thoroughly the category was absorbed rather than developed.
Jurisdictional Note
The challenge principal as a distinct procedural category is a common-law English doctrine. American jurisdictions historically recognized it, but its salience has diminished sharply under modern procedural codes. Federal practice under the Federal Rules of Criminal Procedure and Civil Procedure does not use the terminology; state courts vary in whether their jury-selection statutes preserve any trace of the old classification. Researchers should not assume a jurisdiction's modern "for cause" standards map cleanly onto the historical principal/favor distinction.