In Finnish, you can describe actions that happen by themselves, without a specific actor, using verbs ending in the suffix -tua or -tyä. These are called automative or reflexive verbs.
Automated Actions
These verbs are often derived from standard transitive verbs. For example, avata (to open something) becomes avautua (to open by itself).
As Type 1 verbs, they conjugate normally. Because they describe processes happening to objects, you'll frequently see them in the third-person singular—perfect for describing mechanics and automated systems.
| The heavy door opens. | Painava ovi avautuu. |
| The fridge door closes quickly. | Jääkaapin ovi sulkeutuu nopeasti. |
| Does the engine start up immediately? | Käynnistyykö moottori heti? |
Processes and Natural Phenomena
Because they describe things happening on their own, -tua and -tyä verbs are extremely common when discussing abstract situations, scientific phenomena, and nature. They describe how things take shape or evolve organically.
| The situation is still developing. | Tilanne kehittyy yhä. |
| Ice forms on the lake at night. | Järvelle muodostuu jäätä yöllä. |
Changes of State
This suffix can also express a change in state ("to become" something). For example, from parempi (better) we get parantua (to improve), and from puhdas (clean) we get puhdistua (to become clean).
| His health will improve soon. | Hänen terveytensä parantuu pian. |
| The storm worsens at night. | Myrsky pahentuu yöllä. |
| The forest regenerates, although the fire destroyed it. | Metsä uusiutuu, vaikka tulipalo tuhosi sen. |
| The water becomes clean here. | Vesi puhdistuu täällä. |
