Section 1: Overview

Nouns in Tēsu-Arar inflect through a suffixal case system. Case marking is obligatory for core grammatical relations and follows an ergative–absolutive alignment. The absolutive case is unmarked, while all other cases are expressed through overt suffixes.

Declension is agglutinative and largely regular, with case suffixes attaching directly to the noun stem. Number marking, when present, precedes case marking.

Section 2: Case Alignment

Tēsu-Arar employs an ergative–absolutive alignment. The absolutive case marks both the subject of intransitive clauses and the object of transitive clauses. The ergative case marks the agent of transitive clauses.

As a result, absolutive-marked nouns function as the primary syntactic pivot of the clause, including agreement and control in verbal constructions.

Section 3: Core Cases

The core cases of Tēsu-Arar include the absolutive and ergative. The absolutive case is morphologically unmarked and serves as the citation form of nouns. The ergative case is marked by a dedicated suffix and is used exclusively for agents of transitive verbs.

These cases distinguish argument roles independently of word order, allowing flexibility in constituent placement without loss of grammatical clarity.

Section 4: Oblique Cases

In addition to the core cases, Tēsu-Arar nouns may take a set of oblique cases expressing possession, location, motion, and source. These cases are marked through suffixes that attach outside the noun stem and any number marking.

Oblique cases are productive and may be used both literally and metaphorically, extending spatial meanings to abstract domains.

Section 5: Number and Case Interaction

Number marking on nouns is optional and semantically driven. When present, number suffixes occur between the noun stem and the case suffix. Case marking remains obligatory regardless of number.

This ordering reflects the morphological hierarchy of Tēsu-Arar, in which lexical identity precedes number, and number precedes syntactic role

Section 6: Regularity and Exceptions

The majority of nouns in Tēsu-Arar follow a regular declensional pattern. Irregular forms are rare and typically arise from historical contraction or lexicalized usage rather than productive morphological processes.

Regular declension paradigms represent the default system and are assumed unless otherwise specified.