Learn Finnish: Minä en käytä näitä deodorantteja.

Näitä is the partitive plural form of tämä (this). We use the partitive plural here because the verb käyttää (to use) requires its object to be in the partitive case, and we are talking about multiple deodorants.

Why do both words in näitä deodorantteja have to be in the partitive plural?

In Finnish, demonstrative pronouns (like this, that, these, those) must match the noun they describe in both number (singular or plural) and case. Because the noun deodorantteja is in the partitive plural, the word for 'these' must also take the partitive plural form näitä.

Is the object in the partitive plural because the sentence is negative (en käytä)?

Negative sentences do require a partitive object, but in this specific case, the verb käyttää (to use) is doing the work. It is a 'partitive verb,' meaning its object is always in the partitive case, even in a positive sentence like Minä käytän näitä (I use these).

How do we get deodorantteja from the base word deodorantti?

To form the partitive plural for many words ending in -i, the final -i changes to an -e-, and we add the plural marker -j- followed by the partitive ending -a. So, deodorantti becomes deodorantte- + -ja = deodorantteja. Notice that the double -tt- stays strong!