Why are が and ~て appropriate instead of は and ~た in the following sentence?


I tried translating "Grandpa fell down the stairs and got serious injuries".
Since "Grandpa" is the subject, I used the particle は (wa), and since the
action is in past tense, I used the ~た (ta) ending for 落ちる (ochiru):

> おじいちゃん **は** 階段【かいだん】を落【お】ち **た** 大怪我【おおけが】をした。

After checking my translation attempt, the correction showed おじちゃんが (ojiichan
ga) and 落ちて (ochite):

> おじいちゃん **が** 階段【かいだん】から落【お】ち **て** 大怪我【おおけが】をした。

I know that the particle が (ga) is used for existence of the subject or to
express desire, but I don't need to express existence here. Why is が used
instead of は?

As regards ~て (te), I know that the ending ~て (te) is used for progressive and
imperative tenses, but again I don't need them here. Why is ~て used instead of
~た?

Since I am a beginner in Japanese, I cannot tell if I'm right or wrong. Can
someone explain it to me?




The particle が is used to mark the subject of any sentence. It's not merely a
marker of existence in ある/いる sentences. Although there are times when the
topic and the subject can be interchangeable, in sentences where specific
actions happen, the subject is usually identified clearly. In your sentence,
the subject of the sentence is おじいちゃん, so it is natural to mark that noun with
が.

The て form is also used in a conjunctive manner to connect two clauses. In
your example, there are two clauses (grandpa fell + grandpa was injured).
Using the て form is a simple way to connect those clauses and imply a
relationship between them.

