Ius est ars boni et aequi
“Law is the art of the good and the fair.”
Celsus, quoted in Justinian’s Digest 1.1.1
What does “Ius est ars boni et aequi” mean?
Ius est ars boni et aequi translates as “Law is the art of the good and the fair.”
Law should serve fairness, not only follow rules.
“Ius est ars boni et aequi” word by word
| Latin | English | Grammar |
|---|---|---|
| Ius | law, justice | nominative singular neuter of ius, “law, right”; the subject of the sentence |
| est | is | third person singular present indicative of sum, “I am” |
| ars | art, skill | nominative singular feminine of ars, “art, craft, skill”; the predicate noun |
| boni | of the good | genitive singular neuter of bonus, “good”, used as a noun (“the good”) |
| et | and | conjunction joining boni and aequi |
| aequi | of the fair | genitive singular neuter of aequus, “fair, equal, just”, used as a noun (“the fair”) |
How to pronounce “Ius est ars boni et aequi”
Classical ius begins with a y sound (yoos); Church Latin often makes it yoos too, with the j sound sometimes heard in some traditions. In aequi the Classical ae is like English eye, the Church one like eh. Stress falls on the first syllable of boni and on the first syllable of aequi.
The story behind it
Word for word the line says “Law is the art of the good and the fair”. Ius can mean “law”, “right” or “justice”, so it is often read as a definition of what law is for.
The definition goes back to Publius Iuventius Celsus, a Roman jurist of the late first and early second century AD. It survives because Ulpian, a later jurist, quotes it, and it stands near the very start of Justinian’s Digest (1.1.1), the great sixth-century collection of Roman legal writing.
Through the Digest the phrase passed into the study of law across Europe. Lawyers and students still quote it to argue that law is more than a set of rules: it should aim at what is good and fair.
How to use “Ius est ars boni et aequi”
Fits a law school gift, a lawyer’s office motto, a graduation card or an essay on justice and legal ethics. It suits anyone who wants to say that fairness matters more than rigid rule-following.
- Latin
- Ius est ars boni et aequi
- English
- Law is the art of the good and the fair.
- Source
- Celsus, quoted in Justinian’s Digest 1.1.1
- Era
- Antiquity
- Theme
- Justice
Common mistakes
- Ius is not the same as lex. Ius is law or right in a broad sense, while lex is a specific statute.
- Aequi is not “equal” in the modern sense of identical treatment; it carries the idea of fairness and equity.
- Boni and aequi are genitives (“of the good and fair”), so “Law is the good and fair art” is a wrong reading.
- The line is Celsus’s, not Ulpian’s or Justinian’s; they only preserve it.
Questions about “Ius est ars boni et aequi”
What does “Ius est ars boni et aequi” mean literally?
“Law is the art of the good and the fair.” Ars means skill or craft, so law is treated as a practical skill aimed at goodness and fairness.
Who said “Ius est ars boni et aequi”?
The Roman jurist Celsus, according to Ulpian, who quotes him at the opening of Justinian’s Digest (1.1.1).
How do you pronounce “Ius est ars boni et aequi”?
Classical: yoos est ars BOH-nee et EYE-kwee. Church Latin changes aequi to EH-kwee.
Is “Ius est ars boni et aequi” correct Latin for a tattoo?
Yes, it is the original ancient wording and is grammatically sound. Keep boni and aequi in the genitive and do not alter the word order unless you know why.
More to explore
Translation and grammar checked by Latin Quoter · last reviewed November 2026
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