A relative clause is a subordinate clause that typically modifies a noun or noun phrase. Relative clauses in English can be defining or non-defining and are introduced by relative pronouns (e.g., who, which, that), although these may be omitted or implied [3].
Defining clauses modify the noun or noun phrase with essential information while non-defining clauses modify it with additional, but non-essential, information.
For example:
The three sons of Gárach were waiting at <u>{=html}the ford</u>{=html} which now bears their name. (Defining)
This affliction, ever afterward, seized <u>{=html}all the men of Ulster</u>{=html} who were there that day (Defining)
Ibor was very frightened; he yoked the chariot and tugged at <u>{=html}its skins and coverings</u>{=html}, which Cú Chulaind was sleeping on (Non-defining)
<u>{=html}The one</u>{=html} I love. (Defining, relative pronoun omitted)
Relative constructions are a large and complicated component of Old Irish grammar. In Old Irish, there may be no overt marking of the relative clause such as the pronouns frequently used in English, aside from a relative particle used only in certain contexts.[2]
According to David Stifter:
[T]here are a number of completely different strategies to mark relativity, depending on the person, the dependence/independence of the verb, the infixed pronoun, the relation of the subordinate to the superordinate clause, and the syntactical category of the relativized phrase.
In Old Irish, other forms of subordinate clauses (such as causal, temporal, successive, etc.) are usually treated the same way as relative clauses [2].
For simple verbs, there are separate absolute endings that can express relativity for the 3rd per. sing., 1st per. pl., and 3rd per. pl. For the other persons, a different method must be used. [2]
The aforementioned Old Irish endings derive from the prehistoric relative particle [1][2]:
-yo (suffixed to simple verbs; added to first preverb of compound verbs[2])\ Example:
Gaul. dugiionti-io \'who worship(?)\' (Alise St. Reine)[4]
In Celtiberian the -yo particle was still declinable and had freer sentence placement [4][5]:
iom [Acc. s]; iomui [Dat. s]; ios [Nom. s] (Botorrita I)
Piqueron provides the additional particle -s(e/o)? and suggests that relativity may also be expressed by means of the demonstrative san/sin?.
1. \'Yextis Keltika\', Syntaxe de la phrase complexe, Olivier Piqueron\