This paper explores whether the influence of a grammatically encoded category depends on being obligatory or nonobligatory. This paper tests Slobin’s approach to linguistic relativity. According to Slobin (1996; 2003; 2008), the presence of a grammatically encoded category directs the focus of speakers in the ‘thinking for speaking’ process. Slobin adduces evidence for this claim based on experiments with children in which he focused on the expression of the progressive aspect in various languages, e.g. the present and past continuous in English (is/was running), in comparison with languages that lack such a category. However, Slobin fails to distinguish between obligatory and optional categories. Though both are encoded form-meaning pairings in a language’s grammar (cf. Levinson 2000, Belligh & Willems 2021), only the former must be used in speech in specific contexts. The present article focuses on this distinction and tests Slobin’s account by examining the influence of a grammatical category, such as the ‘aan het construction’ in Dutch, which encodes progressive aspect even though it is non-obligatory in speech. Our findings suggests that Slobin’s thesis should be adjusted: Categories that are encoded and obligatory are generally expressed while categories which are encoded and optional are generally much more ignored. Speakers attend to encoded grammatical categories that are non-obligatory only when the speakers’ attention is explicitly directed to certain aspects of an event.