Subordinate or dependent clauses, which in Common comprise content clauses, relative clauses and adverbial clauses, are clauses contained in a complex sentence that contain their own complete verb phrase structure and typically attach to an element in the larger sentence. In Common, this type of structure is strictly and obligatorily mediated by the use of exactly two relativisers, su and si, which respectively form dependent clauses that can modify a noun phrase or serve as an argument of a verb phrase (or serve in an adverbial role). To an English speaker, this area of Common grammar may seem simultaneously impoverished and overused. Common frequently makes up for its lack of nonfinite verb forms by using dependent clauses instead.

We discussed su and si in our article on Nouns and Pronouns. This article will expand on that basic discussion and go into some more specific cases.

Declensions and Basic Grammar

The two relativisers of Common, normally referred to as 'relative pronouns' by grammarians of Common, are the 'nominal' relative pronoun su and the 'verbal' relative pronoun si. Su and si both decline for case, but do not have number, definiteness or person. They best translate to 'that' or 'which' in English. Other English relativisers like 'when', 'where', 'who', 'whose' etc. are either directly replaced with su and si or else can only be translated with more complicated constructions.

The case of su or si is used to connect the dependent clause to its overall sentence in a way that is specific to each. Su is used to create relative clauses that modify a noun phrase, and the case of su aligns to the role its antecedent plays in the relative clause. Si is used to create content and adverbial clauses, and its case aligns to the role the content clause plays in the sentence overall, typically as an argument of a verb. This manner of marking the role of an antecedent in a relative clause is reminiscent of the strategy employed by German.

A general grammatical comment that is applicable to both broad types of Common dependent clauses is that unlike in English, the use of the relative pronoun is mandatory. In English you could say 'I know he that he is here' or 'I know he is here', and they are basically equivalent expressions. In Common, the only way to say that would be, 'We te pex xi a sy e na spet step se an', with the relative pronoun. This quality is similar to French.

As has been previously noted, dependent clauses have an additional syntactic constraint - the verb needs to be the last element in the clause, although this constraint is somewhat relaxed if the dependent clause is the very last element in the sentence.

In glossing (at least amongst British experts on Common, although this convention predates the collapse of English in the outside world), su is conventionally glossed as RELN and si is glossed as RELV.

Overall the grammatical features of dependent clauses in Common are somewhat 'different', but not terribly alien to speakers of European languages - this is probably due to a mixture of failure of the imagination on Davidson's part, and a natural consequence of the application of the language's underlying syntactic structures around the construction of phrases.

Relative Clauses ('Nominal' su)

A relative clause is a clause that modifies a noun phrase (specifically a noun phrase, since a naked, single-word noun conceptually doesn't exist as an entity in Common). Much as in English, it appears immediately after the noun phrase it modifies. It is conceptually considered to be a modifier of the noun - since the relative pronoun obligatorily takes an object, it has to come out the the 'bracket' of the noun phrase, and it leaves a trace behind, so that when a pronoun is modified in this way, the rule that a head term is mandatory becomes triggered and at minimum a dummy 'yn' must be inserted. Example:

A pocuk xu a ruk jymjym teo slek se an citit.
The child who ate the cookie is happy.

Leaving out honorific and and popular colloquial forms that are often used for third person pronouns, in very formal High Common you could say:

A se an citit.
He/she/it is happy.

To insert the relative clause, a head term would be mandatory, it could be the generic yn, but since we are talking about a person we will use the honorific sy in the example:

A sy xu a ruk jymjym teo slek se an citit.
The gentleperson who ate the cookie is happy.

In Common's 'royal order of modifiers', Common grammarians think the relative clause goes in the 'action' slot in the series, which is the very first position, right after the mandatory article. That means that in the reverse order of modifiers that are removed from the 'bracket' for taking an object, relative clauses have to go last, after all prepositional phrases modifying the noun phrase. This can lead to some ambiguity as to what the relative clause is modifying if there is a noun phrase embedded in a following prepositional phrase, which speakers will generally resolve by restating the antecedent with a pronoun of the right person, number, case and definiteness.

As noted, Common marks the role of the antecedent in the relative clause via the case of the relativiser. Common is not really able to employ gapping as a strategy, given its high tolerance for dropping elements. Further down the accessibility hierarchy, Common arguably does employ resumptive pronouns.

The entire accessibility hierarchy can be relativised. The first three levels are straight-forward, although the case to use for each level is only predictable in the context of knowing the verb in the relative clause:

• Subject: The subject of a verb in Common will be in the Ergative or Absolutive case, and so 'xu' or 'su' will be used.
• Direct Object: The direct object of a verb will be in the Absolutive case, or arguably in the Dative case when it comes to semitransitive verbs, so 'su' or 'ixu' will be used.
• Indirect Object: Indirect objects are in the Dative case and will use 'ixu'. 

The Oblique level and levels below get a little more tricky, but not altogether unfamiliar to English speakers, reflecting the prescriptive forms we have been taught to use in formal English. At this level, the Nominative case is always used, and the preposition of which the antecedent would be the object is pulled in front of the relativiser. This usage also takes over where English would use a word like 'where' as the relativiser. Example:

A Epekwit se an na sifysyn e sun a Paul Wei sy sea lufi.
the(ABS) Epekwit stand(NP.IM) be the(NOM) state at RELN.NOM Paul Wei HON stand(P.IM) born.
Epekwit is the state where Master Paul Wei was born.

Location in this instance is represented by the preposition 'e', which means 'at', and which Common seems to prefer to use whenever possible for locations. This approach works for any instance where the antecedent is the object of a preposition in the relative clause - use 'sun', and pull the preposition in question out of the body of the clause and in front of 'sun'. This is not at all unlike English 'of which' type constructions, but they are mandatory in Common (unlike English, where placing the preposition as a satellite at the end of the clause is usually actually better, idiomatic English). Idiomatic, fluent Common requires this type of construction, and Common uses it much more extensively than English to say things that English would come at in a different way, such as in this example, where English has a word like 'where'.

Skipping a level, the lowest level in the accessibility hierarchy, object of a comparison, is simply a special case of the Oblique. Start with a comparison:

A paluh se an fo akpe erpa na pikki.
the(ABS) dog stand(NP.IM) be GT big against the(NOM) cat.
The dog is bigger than the cat.

Now, embedding that as a relative clause:

A pikki erpa sun a paluh fo akpe se an, se an fo akpe erpa ny skitrem.
The(ABS) cat against RELN.NOM the(ABS) dog GT big stand(NP.IM) be stand(NP.IM) be GT big against a(NOM) mouse.
The cat the dog is bigger than is bigger than a mouse.

The word handling the 'than' function in Common comparisons, 'erpa' ('against') gets pulled in front of 'sun' like a normal preposition.

The Genitive level is interesting, and reflects another possible break with expected natural language behaviour in Common, since the expectation of the accessibility hierarchy is that if a level is accessible in a language, all the levels above that level are also accessible. However, in Common, the Object of Comparison level is clearly accessible, and the Genitive level is at least ambiguous.

 As has been noted before, possessive structures were weakly built into Common and mostly kluged into existence by later speakers, with the null preposition possessive perhaps being the default. We'll look here at the null preposition structure as perhaps being the best representative of the 'Genitive' in the hierarchy.

Start with a simple possessive:

We nox sifre ija meritka na pikki.
I(ABS) go(NP.IM) familiar the(DAT) owner ∅ the(NOM) cat.
I know the cat's owner.

For our example, we will translate, 'The cat whose owner I know ate the mouse.' Common lacks a word like 'whose' to handle a sentence like this. You could say:

Ja pikki sun we ija mertika nox sifre tene slek a skitrem.
The(ERG) cat RELN.NOM I(ABS) the(DAT) owner go(NP.IM) familiar hit(NP.PF) eat the(ABS) mouse.

This is a completely licit and idiomatic thing you can say, relying on context to make it clear to the listener that the cat's owner is meant. In fact, this would be the usual thing to say, evading the possessive construction altogether. However, it is not explicit that the relationship between the owner and the cat is that the owner belongs to the cat. A relative clause with 'sun' with the role of the antecedent being ambiguous is completely licit in Common.

It is possible to make the relationship explicit in Common, but it would be done essentially with a resumptive pronoun, with the idiomatic antecedent expression na spe'n serving in that role. So:

Ja pikki sun we ija mertika na spe'n nox sifre tene slek a skitrem.
The(ERG) cat RELN.NOM I(ABS) the(DAT) owner ∅ the(NOM) ANTECEDENT go(NP.IM( familiar hit(NP.PF) eat the(ABS) mouse.

This expression using na spe'n as a kind of resumptive pronoun is completely clear about the role of the cat in the relative clause as possessing the owner.

Verbal Dependent Clauses ('Verbal' si)

In Common, any time a clause with its own internal verb structure acts as an argument to a verb in a main clause, it is mandatory for the clause to be introduced with the relativiser si. the case of si corresponds to the role of the clause as a whole on the verb. In any case where such a clause does not have a direct role on the verb but is part of a construction serving an adverbial role, the nominative sin would be used.

These structures are mostly very straight-forward, but some explanation is merited for the use of the RELV.NOM (Nominative) form sin, which is used in forming adverbial clauses. To see where it would be used, let's look at real world example, from the first line of the Globalist Manifest: A atenys Onpa xu wez te speos arte tene faj can xeppe, hanja a spet yn nox hufep ija ejálys etríjusyn u sin ti mawa. This translates in fluent English to, 'The unified world that we enjoy today has been very hard-won, and constant vigilance is required to maintain it,' and in more literal, word-for-word translation as, 'The united globe that we today profit from has been very hard won and needs constant vigilance so that would protect.' Breaking down the Common:

A atenys Onpa xu wez te speos arte tene faj can xeppe, hanja a spet yn nox hufep ija ejálys etríjusyn u sin ti mawa.
the(ABS) united globe RELN.ERG we(INCL.ABS) hit(NP.IM) today profit hit(NP.IM) very hard win and-then the(ABS) this one go(NP.IM) need the(DAT) constant vigilance to RELV.NOM hit(NP.IM.IRREAL) protect.

This example shows a common real-world use of 'sin' in bold, and an example of the phenomenon of Common using dependent clause structures to make up for its lack of infinitives. The object of a preposition has to be a noun phrase in the nominative case, full stop. In this instance, though, 'u' 'to', is being used in its sense of 'in order to;, and for this expression, it requires verbal morphology in its object. The forms of 'si' make a verb phrase and its arguments function as a noun phrase with respect to a governing element in a main clause. The nominative form, 'sin', serves this role as the object of a preposition, making a complex structure with verbal morphology a licit object of a preposition.