An adverbial relative clause is a free relative clause whose higher nominal has the function of a place, time or manner adjunct in the matrix. In these cases, the semantic core is a ‘place’, ‘time’ or ‘manner’, and the higher nominal inherits this feature. Thus, semantic category and semantic function coincide in these cases.

Like other free relative clauses, adverbial relative clauses come in two varieties, as a light-headed and a headless relative clause. Again, the former may take the form of a correlative diptych. is an example.

A full description of the relative construction of would mention the following categories and functions:

1. The semantic core of the relative clause – the light head – is a place.
2. The referent formed by the relative clause and represented by the demonstrative in the matrix is a place.
3. The syntactic function of the light head is ‘local adjunct’.
4. The syntactic function of the resumptive in the matrix is ‘local adjunct’.

While the identity of the category of the light head and the higher nominal (#1 and 2) is necessary, the identity of the syntactic functions (#3 and 4) is not. It is, however, highly natural and leads to maximum coincidence of category and function in both clauses.

Next, an adverbial relative clause may be a non-correlative light-headed relative clause. The English translations of some of the following examples suffice to illustrate it:

The subordinate clause in both and is introduced by a formative that stems from an interrogative pro-adverb. The declension paradigm of English interrogative or relative pronouns does not include a locative, let alone a temporal case. Therefore these adverbial forms got separated from the relative pronouns, get fossilized and become members of the set of subordinative conjunctions. At the same time, the subordinate clause ceases to be a relative clause and becomes an adverbial clause at the side of causal and other subordinate clauses that are in different interpropositional relations with the main clause.

Since the adverbial relative clause is a specific case of a free relative clause, we also find adverbial relative clauses with ‘formal nouns’ in head position. English uses them for manner clauses, as in .

and illustrate this for local and temporal adverbial clauses.

Just like Turkish postpositions develop into case suffixes, such formal nouns develop into suffixal adverbial subordinators. Thus, yerde terminating a subordinate clause becomes equivalent to the conjunction ‘where’, and zaman starts functioning as ‘when.’

The target of this grammaticalization process is represented by the headless adverbial relative clauses and .

In , the locative suffix is appended to a headless relative clause, producing a local clause. The same affix in produces a conditional clause. This is, thus, an alternative way how certain adverbial clauses may be based on relative clauses.