Learn Hardcore Japanese: kyuuni ame ga hurihazimemasita.

急に
- Fairly neutral and common in both speech and writing.
- Often used for changes in state: 急に寒くなった “It suddenly became cold,” 急に雨が降り始めた “It suddenly started to rain.”
突然 (とつぜん)
- Slightly more formal or written-sounding.
- Often used for more dramatic or unexpected events: 突然、電話が鳴った “The phone suddenly rang.”
いきなり
- Very colloquial/spoken.
- Often used when something happens abruptly or without preparation, sometimes with a feeling of “out of nowhere”:
  いきなり雨が降り始めた “It just suddenly started raining (out of nowhere).”

In this sentence, 急に is a natural, neutral way to say “suddenly.”

Why is 雨 marked with が and not は or を?

が marks the grammatical subject of the sentence. Here, 雨 (rain) is the thing that is starting to fall, so it is the subject:

雨が降り始めました。
“Rain started to fall.” → “It started to rain.”

Why not the others?

は: marks a topic, not necessarily the subject. You could say 雨は降り始めました, but then “rain” is already a known or contrastive topic (e.g., compared with something else). The neutral description of what happened now is usually 雨が.
を: marks a direct object. The verb 降る doesn’t take a direct object in this sentence; rain itself is what is doing the action of falling, so が is correct.

Why is there no word for “it” in “It suddenly started to rain”?

Japanese normally doesn’t use a dummy subject like English “it” in weather sentences. Instead, the weather phenomenon itself becomes the subject:

English: “It is raining.”
Japanese: 雨が降っています。 (“Rain is falling.”)

So in 急に雨が降り始めました, 雨 is the subject. English adds a dummy “it”, but Japanese doesn’t need that; the sentence literally says “Suddenly, rain started to fall.”

What is 降り始めました made from, and how is this “start to do X” pattern formed?

降り始めました is a combination of:

Verb 降る (ふる) “to fall” (used for rain, snow, etc.)
Its ます-stem (verb stem): 降り
The verb 始める (はじめる) “to begin, to start”
In polite past form: 始めました

Pattern:

V-ます stem + 始める = “to start to do V”

Examples:

降り始める – “to start to rain/fall (rain, snow, etc.)”
食べ始める – “to start eating”
勉強し始める – “to start studying”
話し始める – “to start talking”

Then put 始める into the appropriate tense/politeness:

降り始めます – (polite, non‑past) “starts to rain / will start to rain”
降り始めました – (polite, past) “started to rain”

If the rain is starting now, why is it 始めました (past tense) and not something like present tense?

In Japanese, the past polite form 〜ました is used once an event or change of state has begun or completed — even if its result continues now.

降り始めました focuses on the moment the raining began. It means:

“(It) has started to rain”
“(It) started to rain (just now / a moment ago)”

English might describe this with either simple past (“started”) or present perfect (“has started”), but in Japanese it’s just the normal past form 始めました.

So the sentence is describing a change that has already occurred: the rain has already begun at the time of speaking.

What is the difference between 雨が降りました, 雨が降り始めました, and 雨が降ってきました?

They all involve rain but focus on slightly different things:

雨が降りました。
- “It rained.”
- Neutral statement that rain fell at some time. It doesn’t emphasize the start.
雨が降り始めました。
- “It started to rain.”
- Highlights the beginning of the rain. Good when you want to talk about the moment the rain starts.
雨が降ってきました。
- Literally “Rain has come to falling,” commonly translated “It has started raining / It’s begun to rain.”
- Focuses more on the rain coming toward you / arriving here now.
- Often used when you suddenly notice it starting: あ、雨が降ってきた “Oh, it’s started raining (here now).”

In many everyday contexts, 降り始めました and 降ってきました can both be translated “it started to rain,” but 降り始めました sounds a bit more neutral/description-like, while 降ってきました feels a bit more immediate or experiential.

Can 急に go in other positions in the sentence, or must it be at the beginning?

急に is an adverb, so it is fairly flexible in position as long as it’s close to the verb phrase it modifies. These are all natural:

急に雨が降り始めました。
雨が急に降り始めました。

The nuance is very similar; both mean “It suddenly started to rain.” The most common in writing is probably the original order, but 雨が急に降り始めました is perfectly fine in speech.

Generally, adverbs like 急に, とても, あまり, etc. can go before the verb phrase, after the subject, or at the start of the sentence, depending on emphasis and style.

What politeness level is 急に雨が降り始めました? How would it look in plain (casual) form?

急に雨が降り始めました。 is in polite form because of 〜ました.

To make it plain (casual):

Polite: 降り始めました
Plain past: 降り始めた

So the casual version is:

急に雨が降り始めた。

This would be used with friends, family, etc. The meaning is the same; only the politeness changes.

How do you read 急に雨が降り始めました aloud (pronunciation)?

The reading is:

急に – きゅうに (kyuu ni)
雨 – あめ (ame)
が – が (ga)
降り – ふり (furi)
始めました – はじめました (hajimemashita)

All together:

きゅうに　あめが　ふりはじめました。
kyuu ni ame ga furi hajimemashita.

How would I negate or make a question with this pattern V-stem + 始める?

Use 始める like a normal verb:

Negative (polite)
- Pattern: V-stem + 始めません
- Example:
  急に雨が降り始めませんでした。
  “It did not suddenly start to rain.” (a bit unusual in real life, but grammatically fine)
Question (polite)
- Pattern: V-stem + 始めましたか
- Example:
  急に雨が降り始めましたか。
  “Did it suddenly start to rain?”
Casual negative / question (plain form)
- Negative: 降り始めなかった
- Question (spoken, rising intonation): 急に雨が降り始めた？
  “Did it suddenly start raining?”

The key is that 始める itself is a normal verb, so you conjugate 始める (始めない, 始めました, 始めますか, etc.) while keeping the first verb in its ます‑stem (降り, 食べ, 話し, etc.).