Learn Finnish: Äiti siivosi keittiön puhtailla käsineillä. - The mother cleaned the kitchen with clean gloves.

The basic word is puhdas. For words ending in -as, the stem changes to end in -aa-, making puhtaa-. To make the plural adessive form, we add the plural marker -i- and the case ending -lla. The double -aa- drops one -a- when the plural -i- is added, resulting in puhtailla.

How is the adessive plural ending added to käsine (glove)?

For words ending in -e like käsine, the stem doubles the last vowel to become käsinee-. When we add the plural -i- and the adessive ending -llä, the double -ee- drops one -e-, giving us käsineillä. Notice that both the adjective and the noun must match cases, which is why both words have the plural adessive ending!

Why is the adessive case (-illa/-illä) used here to mean "with"?

The adessive case, which you normally use to mean "on" or "at", is also the standard way to express a tool or instrument used to do an action in Finnish. So puhtailla käsineillä literally means "by means of clean gloves" or "using clean gloves".

Why is the kitchen written as keittiön instead of the basic form keittiö or the partitive ?