An oath is a binding act of speech that places the speaker under obligation before divine authority and communal custom. Oaths are taken seriously and used sparingly. Swearing an oath commits the speaker to a chosen course, binding intention, outcome, and responsibility through speech.
Because no complete Gaulish oath formula survives, our oath practice is a modern reconstruction informed by the work of John T. Koch, who provides comparative evidence.
Early Irish sources preserve the clearest example of a Celtic oath formula: tongu do dia toinges mo thúath (“I swear by the god by whom my people swear”). As discussed by John T. Koch, this formula shows how Celtic oaths bind the speaker through indirect divine authority while grounding obligation in communal custom. The deliberate avoidance of naming the enforcing deity distinguishes oath-speech from coercive or magical language and reflects a formal, socially recognized act of binding.
Koch observes that tynghaf tynghet has been interpreted as “I swear a destiny on you,” reflecting a semantic range in which swearing, binding, and fate/destiny are closely connected. He further compares the Welsh verb tyngu (tynghaf) with Old Irish tongu (“to swear”), suggesting that both shared a Celtic linguistic heritage of sworn or pledging speech, despite differences in grammatical form and social context. He notes that the Welsh expression tynghaf tynghet parallels the Old Irish oath formula in function, even though it is not a legal oath formula in the same sense. It operates as a declarative, oath-like statement of binding intent.
Gaulish evidence preserves the same concept through magical binding language rather than full oath formulas. The Chamalières tablet contains the expression toncnaman toncsiiontio, built on the root tonc- (“to swear, to bind”). This phrase demonstrates that Gaulish possessed a formal vocabulary of oath-binding speech, even though complete oath sentences are not found. This supports the broader Celtic pattern in which solemn speech creates obligation through recognized authority.
Our oath formula adapts this older Celtic structure into Gaulish while remaining honest about its modern, reconstructed nature.
The Gaulish word for an oath is oitos, referring to a formal and socially recognized act of swearing. Alongside this, Celtic languages preserve a group of related words built on the root tonc-, connected with swearing, binding, and fate. In Proto-Celtic, the verb tong-o- means “to swear,” while the noun tonketo- means “destiny” or “fate.” Although these are treated as separate forms by scholars, their meanings are closely related.
In Gaulish, the word toncnaman (“to swear an oath”) is directly attested in inscriptions, showing that formal oath-binding language existed. A related form, tonceton (“fate, luck”), is reconstructed, further reflecting the close association between sworn speech and the shaping of future outcomes.
Oath formula:
tongūmī Dēuū io toutā mou tonget
“I swear by the God that my tribe swears by”
tongūmī Dēuobis io toutā mou tonget
“I swear by the Gods that my tribe swear by”
- tong- (“swear, take oath”) + ū- (1st person singular ending) + mī (1st person singular present indicative)
- Dēu- (“god”) + -ū (ablative singular ending)
- io (relative clause particle – “that, which”)
- toutā (“tribe” – nominative singular)
- mou (genitive singular of 1st person singular pronoun showing possession – “my”)
- tong- (“swear, take oath”) + -et (3rd person singular present indicative)
In our worldview, an oath (oitos) is a binding act of speech that commits the speaker to a determined course within divine and communal order. An oath does not compel the gods or bind others; it binds the one who speaks. Obligation is fixed through recognized authority and custom rather than personal intent or emotion. Rooted in the tonc- family of binding speech, oath-taking stands close to the idea of destiny—not as fatalism, but as chosen necessity. Once an oath is sworn, the future is no longer fully open. For this reason, oaths are used sparingly and treated as virtuous acts that deliberately limit freedom in the name of honor, order, and right conduct.
In relation to the gods, Gaulish evidence suggests a clear distinction between vows and oaths. Gallo-Roman inscriptions preserve votive language in which offerings are dedicated to named deities in response to divine action, reflecting a reciprocal and conditional structure. Oaths, by contrast, are binding declarations concerning future behavior, grounded in divine authority and communal custom rather than exchange. While an oath may be violated, it cannot be undone; its obligation remains regardless of later intent.
Within our bessus, this distinction is also reflected in language. Our word for oath is oitos. Our word for vow is īueron, the verbal noun of īueret (“to promise, make an offering, give thanks”). A vow is a voluntary and conditional act directed toward a specific god, often taking the form of dedication or offering in response to divine aid. Unlike an oath, a vow does not fix destiny or bind the speaker under communal enforcement; it expresses devotion, reciprocity, and gratitude. Vows are appropriate for petitions and offerings, while oaths are reserved for matters of honor, truth, and lasting obligation.
Notes
- Thanks to Cunolugus Drugaisos for the language help.
- John T. Koch – Further to tongu do dia toinges mo thuath, &c
Bessus Nouiogalation 