aki... az...

In this advanced syntactic structure, the demonstrative az acts as a placeholder (a correlate) and the true syntactic head of the main clause argument. This pattern applies equally to people (aki... az...), inanimate objects or concepts (ami... az...), and specific items singled out from a group (amelyik... az...).

1. Independent Declension
Because the pronouns belong to different clauses, they take suffixes based on their local verbs. For example, in Azt hívtam meg, akivel tegnap találkoztunk (I invited the one whom we met yesterday), az becomes accusative azt (object of 'invited'), while aki becomes instrumental akivel (complement of 'met with').

2. Phonological Assimilation
When az takes case suffixes beginning with a consonant, assimilation occurs. Either the 'z' assimilates to the suffix consonant (e.g., az + ban = abban), or the suffix consonant assimilates to the 'z' (e.g., az + val = azzal, due to v-assimilation). See Demonstrative Assimilation.

3. Number Agreement
The correlative pronouns must agree in number. If the referent is plural, both pronouns must take the plural suffix -k before any case endings, resulting in pairs like azok... akik..., azok... amik..., or azok... amelyek....

4. Generic Meaning and Word Order
This pattern is frequently used for generic, universal statements equivalent to "anyone who" or "whoever". Additionally, the word order is highly flexible. The relative clause frequently precedes the main clause, especially for topicalization or generic statements (e.g., Aki keres, az talál.). The relative clause can also be embedded directly inside the main clause, immediately following the demonstrative correlate (e.g., Az, aki keres, talál. or Azt, akivel tegnap találkoztunk, meghívtam.).

5. Pronoun vs. Determiner
It is important to distinguish the standalone pronoun az from the demonstrative determiner. If a noun is explicitly stated in the main clause, az acts as a determiner and must be followed by the definite article a/az (e.g., Az a fiú, aki... - That boy who...). The correlative pronoun pattern, however, stands alone without a following noun.

6. Omission of the Demonstrative
Hungarian allows the omission of az if it is in the nominative or accusative case (e.g., [Azt] hívom, akit akarok). For oblique cases (like dative or instrumental), az is generally obligatory if the main clause and relative clause require different cases. However, it can be dropped if there is case matching—meaning the relative pronoun carries the exact same oblique case (e.g., [Annak] adom a könyvet, akinek akarom.).

7. Postpositions
When the demonstrative az takes a postposition, it merges into a single word and the 'z' assimilates or drops (e.g., az + mellett = amellett). In contrast, the postposition remains a separate word after the relative pronoun (e.g., aki mellett). For example: Amellett állok, aki mellett te. (I stand beside the one whom you stand beside).