Learn Hardcore Japanese: sono akai bousi ha watasi no huku ni awanai kara, betu no iro wo sagasu. - That red hat doesn’t match my clothes, so I’ll look for another color.

この赤い帽子 = “this red hat (near me / the speaker)”
その赤い帽子 = “that red hat (near you / the listener, or the one you just mentioned)”
あの赤い帽子 = “that red hat (far from both of us, or not immediately present but known)”

In conversation, その is also often used when both people already know which hat is being discussed (even if it’s not physically near the listener). It marks something that is “already in shared awareness.”

Why is it 赤い帽子 and not 赤帽子 or 赤の帽子?

赤い is an i-adjective, and i-adjectives normally go directly before a noun to modify it:

赤い帽子 = “a red hat”
大きい家 = “a big house”

赤帽子 would sound like a set phrase, a brand name, or a very compressed compound noun; it’s not the normal way to say “red hat.”

赤の帽子 is possible, but it’s less common and feels a bit more like “a hat of red (color),” sometimes used when you’re contrasting colors (e.g. 赤の帽子と青の帽子 “the red hat and the blue hat”). In everyday speech, 赤い帽子 is the standard choice.

Why is は used after 帽子: その赤い帽子は? Could we use が instead?

は marks the topic: what the sentence is about.
Here, the sentence is “about” that red hat:

その赤い帽子は = “As for that red hat,” / “That red hat…”

If you said その赤い帽子が私の服に合わない, it’s still grammatical, but:

が emphasizes it as the subject of the statement, sometimes sounding more like you’re identifying which thing doesn’t match.
は is more neutral here and natural when you’re already talking about that hat.

In context like shopping and commenting on items, は is the usual choice: you’ve already introduced the hat and are now describing it.

Why is it 私の服に合わない and not 私の服と合わない or something else? What does the particle に do here?

With the verb 合う (to match / to go well with), the thing something matches typically takes に:

A は B に合う = “A matches B” / “A goes well with B”

So:

その赤い帽子は私の服に合わない
= “That red hat doesn’t match my clothes.”

Here, 私の服に marks the standard or counterpart that the hat is being compared to.

と合う can also appear in some contexts, but 服に合う, 靴に合う, 〜に合う is the common and natural pattern for “to suit / to match” something.

What exactly does 合わない mean here, and how is it formed from 合う?

合う is an u-verb that, among other meanings, can mean “to suit / to match / to go well with.”

To make the plain negative of an u-verb:

Take the dictionary form: 合う
Change the u sound to a
- ない: 合わない

So:

合う = “matches / goes well (with)”
合わない = “does not match / does not go well (with)”

In this sentence, 合わない means “doesn’t go well with” or “doesn’t suit” your clothes.

What is the role of から in 合わないから? Does it mean “because”? Why does it come in the middle instead of the beginning like in English?

Yes, から here means “because / since.” It attaches to the reason clause:

その赤い帽子は私の服に合わないから
= “Because that red hat doesn’t match my clothes,” …

In Japanese, the usual pattern is:

[Reason] から、[Result].

In English we can put “because” either first or in the middle, but Japanese almost always puts から (or ので) after the reason clause.

So the structure is literally:

[The red hat doesn’t match my clothes] because, [I’ll look for a different color].

Could we replace から with ので here? Is there any difference?

You can say:

その赤い帽子は私の服に合わないので、別の色を探す。

ので also means “because / since.”

Nuance:

から is more neutral and direct; common in casual speech.
ので is often a bit softer and more formal / polite-sounding, especially with です／ます:
- 合わないので、別の色を探します。

In casual, spoken Japanese between friends, から is more typical. Both are grammatically fine here.

In 別の色, what does 別 mean, and how is it different from 他の (ほかの)?

別 (べつ) means “separate / different / another type.”
別の色 = “a different color” / “another color.”

他の (ほかの) also means “another / other,” so:

別の色
他の色

Both can be understood as “a different color,” and in many everyday contexts they’re interchangeable.

Very roughly:

別の can sound more like “separate, distinct, not the same one.”
他の can sound more like “some other one (besides this).”

But here, for everyday speech while shopping, 別の色 is completely natural and common.

Why is there an を before 探す: 別の色を探す? What does 探す mean exactly?

探す (さがす) is a transitive verb meaning “to look for / to search for.” It takes a direct object marked by を:

〜を探す = “to look for 〜”

So:

別の色を探す
= “(I will) look for a different color.”

Don’t confuse it with 見る (to look at).
探す is about searching, not just looking:

映画を見る = “to watch a movie”
映画館を探す = “to look for a movie theater”

Who is the subject of 探す? Why isn’t 私 repeated?

In Japanese, it’s very common to omit the subject when it’s clear from context.

Earlier in the sentence you have 私の服 (“my clothes”), and the person speaking is the one evaluating the hat. It’s natural to assume:

(私は) 別の色を探す。
= “I will look for another color.”

Repeating 私 would sound unnatural or overly explicit in casual Japanese, like saying “I, I, I” too much in English. Context tells us it’s the speaker who is going to look for another color.

Why are both verbs in the plain form (合わない, 探す) instead of polite forms like 合いません and 探します?

The sentence is in plain (informal) style, which uses:

nonpast: 合う → 合う, 探す → 探す
nonpast negative: 合わない

To make it polite, you’d say:

その赤い帽子は私の服に合わないので、別の色を探します。
or
その赤い帽子は私の服に合わないから、別の色を探します。

Use plain form with friends, family, or in your own thoughts; polite form (〜ます／です) in more formal situations or with people you don’t know well.

Why is 探す in the non-past form if it means “I will look for” another color?

Japanese non-past form covers both present and future, depending on context.

毎日コーヒーを飲む。
= “I drink coffee every day.” (habitual present)
明日コーヒーを飲む。
= “I will drink coffee tomorrow.” (future)

Here, the structure [Reason] から、[Verb]. naturally implies a future, intentional action:

合わないから、別の色を探す。
= “It doesn’t match, so I’ll look for a different color.”

Context (shopping, making a decision now) tells us it’s a future intention, even though the form is just the plain non-past.