Learn Hardcore Esperanto: Kiam la vetero fariĝas malvarma, ni devas porti jakon. - When the weather becomes cold, we must wear a jacket.

Fariĝas means “becomes” or “gets,” indicating a change in state. In this sentence it shows that the weather is changing from its current condition to a colder one. Using estas would simply state that the weather is already cold, rather than emphasizing the process of becoming cold.

What is the role of the -n ending in jakon?

In Esperanto, the -n ending marks the direct object in a sentence. Here, jakon (from jako) is the object of porti. This ending tells us that the jacket is what we must wear—the noun receiving the action of the verb.

Why is porti translated as “wear” in this context, even though it can also mean “carry”?

While porti can mean both “to carry” and “to wear,” the context here (talking about clothing) makes its meaning clear. In everyday Esperanto, when referring to clothing, porti is understood as “to wear,” much like how English speakers say they "wear" a jacket rather than "carry" it.

What does Kiam signify at the beginning of the sentence?

Kiam simply means “when.” It introduces the time clause and sets up the condition under which the main clause applies, namely, the moment when the weather becomes cold.

Why is the definite article la used with vetero but there’s no article before jakon?

In Esperanto, la is the only definite article and is used when referring to something specific or generally known, like la vetero (“the weather”). There is no indefinite article, so when referring to nonspecific instances—such as wearing “a jacket” in general—the noun appears without an article as in jakon.