Vocab: muutuma - to change
to change; to become; to become different; to change into something telse; (in grammar, about a word:) to appear in different forms
Building blocks
muut- → verb stem (change / become)
-u- → indicating that something becomes / changes by itself
-ma → infinitive ending
So the core meaning is a change that happens to the subject, not something the subject does to something else.
Compare:
muutma → to change something (active, transitive)
muutuma → to become / to change (intransitive)
How to use it
What to remember
What something changes into is expressed with the translative case (-ks)
With muutuma, the thing you change into is expressed as:
milleks → nouns (thing / role / object)
milliseks → adjectives (state / quality / kind)
Example
Õu muutus vihmasajus poriseks ja libedaks
Literally: “Yard became rain-in muddy-into and slippery-into”
Idiomatically: “The yard became muddy and slippery in the rain”
Õu - Noun - Nominative Singular: "Yard"
muutus - Verb - 3rd Person Singular, Past Tense: "became"
vihmasajus - Noun - Inessive Singular: "in rain"
poriseks - Adjective - Translative Singular: "into muddy"
ja - Conjunction - Indeclinable - "and"
libedaks - Adjective - Translative Singular: "into slippery"