Learn Finnish: Älä aja mopolla metsässä! - Do not ride a moped in the forest!

In English, you "ride a moped" (making it a direct object). In Finnish, you are expressing the means of transport. You use the Adessive case (-lla) to say you are driving "by means of a moped", similar to autolla (by car) or bussilla (by bus).

English uses "ride" for a moped, but the Finnish verb is "ajaa" (to drive). Can "ajaa" be used for riding?

Yes! In Finnish, ajaa is the standard verb for operating almost any wheeled vehicle. Whether it is a car, a bicycle, or a moped, you use ajaa. The English translation changes to "ride" simply because that sounds more natural to English speakers.

Why is the command "Älä aja" instead of "Et aja"?

Älä is the negative imperative verb used for commands meaning "Do not". Et aja is a regular statement meaning "You do not drive". For a negative command, you always pair älä with the stem of the main verb, which is aja here.

Why does "metsässä" use the Inessive case (-ssä) here?

The Inessive case expresses being physically inside a place or space. Here, the action of riding is taking place inside the forest. If the sentence were about driving into the forest, you would use the Illative case (metsään).