The conceptual proximity and formal interrelation of the categories aspect and Aktionsart complicate the theoretical definition of the notions of aspect. Nevertheless, aspect and Aktionsart form two different categories that cannot be interchanged.
Aspect is a grammatical category marked by grammatical operators (e. g. morphemes, particles) in the verb stem. It provides information about the internal structure of a defined period of time. An example of grammatical aspect is the suffix - ing in English or affixes in the Slavic languages.
In contrast, Aktionsart is a lexico-semantic category that defines the time interval structure of a situation. Durativity, telicity and iterativity are examples of types of Aktionsart.