Definition
Half blood describes the relationship between two persons who share only one common ancestor — typically one parent — rather than both parents. Two individuals are of the half blood when they descend from the same father but different mothers, or from the same mother but different fathers. By contrast, persons who share both parents are of the whole blood.
The concept matters principally in the law of intestate succession, where it governs whether a collateral heir — a sibling, half-sibling, aunt, uncle, or cousin — inherits from a decedent's estate on equal footing with whole-blood relatives, at a reduced share, or not at all. At common law, half-blood collaterals were disfavored and could be entirely excluded from inheritance by a whole-blood relative of the same degree of kinship. Modern statutes have largely abandoned that exclusion, but the distinction has not disappeared entirely: several jurisdictions still treat half-blood heirs differently from whole-blood heirs in specific circumstances, particularly in ancestral or inherited property rules.
Common Language
Modern common usage (Wiktionary): A person who shares one parent with another; a half-sibling. Also used informally to mean someone whose parents are of different races.
Historical common usage (Webster's 1913): The relation between persons born of the same father or of the same mother, but not of both. Also used to describe a person of mixed racial parentage.
The legal meaning tracks the ordinary meaning reasonably closely when the term refers to shared parentage — but the common usage stops there. In law, half blood is not merely a description of family relationship; it is a term of art that has historically determined inheritance rights, priority among heirs, and the capacity to take real property from a decedent. The racial connotation found in both Webster's 1913 and Wiktionary has no place in modern legal usage and is legally irrelevant.
Common Confusion
Half blood is sometimes loosely treated as synonymous with half-sibling in everyday speech, which is accurate as far as it goes. The legal confusion runs in the other direction: researchers working with older materials may encounter statutes or treatises that treat half blood as a near-absolute bar to inheritance rather than a mere modifier of degree. That older common-law rule — exclusion, not reduction — does not reflect current law in most U.S. jurisdictions and should not be imported into modern analysis. The term should also be distinguished from collateral heir generally: all half-blood collaterals are collateral heirs, but not all collateral heirs are of the half blood.
Why It Matters in Research
The principal research trap with half blood is chronological: the common-law rule of total exclusion was the baseline for centuries of English and early American authority, but American jurisdictions moved away from it at different times and in different ways. A treatise or digest written before a state's intestacy reform may describe a rule that no longer operates. Researchers should verify the applicable statute directly rather than relying on secondary synthesis.
A secondary trap involves ancestral or lineage property. Some jurisdictions retained a modified half-blood rule specifically for property that descended to the decedent from an ancestor — the logic being that such property should trace back through the bloodline from which it came. This creates a situation where a half-blood sibling may inherit equally with a whole-blood sibling in general intestacy but be excluded or reduced when the estate consists of property the decedent inherited from their shared parent's side.
In historical sources, the French law terms demy-sangue or demy-sanke appear in older English materials and in early American legal dictionaries. Researchers in colonial or early republic sources should recognize these as direct equivalents of half blood.
The term also surfaces in adoption and legitimacy contexts. Whether an adopted child stands as whole blood or half blood relative to the adoptive family's biological children varies by statute and affects both inheritance and, historically, certain family law determinations.
Historical Dictionary Support
Burrill's Law Dictionary defines half blood as "[t]he blood of one parent only; blood on the father's or mother's side only," describing it as "a term applied to collateral relations, when descended from a single person, who is the only ancestor common to them both." Burrill cites Blackstone directly (1 Bl. Com. 194), which reflects the common-law foundation of the concept. The Burrill entry is accurate as a description of the relationship but does not fully convey the legal consequence that Blackstone's era attached to it — namely, that half-blood collaterals were barred from inheriting land in preference to whole-blood relatives of equal degree.
What historical dictionaries of this period uniformly omit is the statutory trajectory: the movement in American jurisdictions throughout the nineteenth and twentieth centuries toward either equalizing half-blood and whole-blood heirs or reducing (rather than eliminating) the half-blood heir's share. A researcher relying solely on Burrill or contemporaneous sources will find the relationship defined accurately but the operative legal consequence described in terms that may no longer apply.
Jurisdictional Note
American jurisdictions vary significantly. Many states now provide that half-blood relatives inherit equally with whole-blood relatives of the same degree. Others provide that a half-blood relative inherits half the share of a whole-blood relative. A smaller number retain modified rules for ancestral property. English law historically treated half blood as a complete bar to inheritance of real property, a rule that influenced early American common law but was largely superseded by statute.