Learn Hardcore Japanese: mise no iriguti ha semai ga, deguti ha hiroi. - The store’s entrance is narrow, but the exit is wide.

は marks the topic and is contrastive here. The pattern A は X が、B は Y sets up a comparison between two topics (entrance vs. exit). So 入口は and 出口は each introduce what we’re talking about, highlighting the contrast between them.

The が after 狭い — is that the subject marker?

No. Here が is a conjunction meaning but/though. It connects two clauses in a somewhat formal/neutral style. Subject-marking が appears right after a noun (e.g., 雨が降る). Conjunctive が comes after predicates (verbs/adjectives), as in 狭いが….

Could I use けど or でも instead of が?

けど / けれど(も): More conversational. Example: 店の入口は狭いけど、出口は広い。
でも: Works best at the start of the second sentence. Example: 店の入口は狭い。でも、出口は広い。
が: Slightly more formal/written feel. All three convey contrast.

Why is there a の between 店 and 入口?

の links two nouns, making an attributive or possessive-like phrase: 店の入口 = the store’s entrance. Compare:

店の入口は狭い (the store’s entrance is narrow)
店に入口がある (there is an entrance at the store)

Is 入口 or 入り口 correct? Which should I use?

Both are correct. 入口 is the modern, common spelling; 入り口 is also acceptable and transparently shows the verb stem 入り plus 口. You’ll see both in the wild.

Why is 口 read ぐち (not くち) in 入口 and 出口?

That’s due to rendaku (consonant voicing) in compounds: 口 (kuchi) → ぐち (guchi). Common examples:

出口でぐち
入口いりぐち
東口ひがしぐち Not every compound triggers rendaku, but these do.

Why is there no です? How do I make it polite?

I-adjectives like 狭い and 広い can predicate a sentence without a copula in plain style. To make it polite:

店の入口は狭いですが、出口は広いです。 You can also say: 店の入口は狭いですけど、出口は広いです。

What’s the difference between 狭い and 細い?

狭い: narrow/cramped for spaces/areas (rooms, roads, entrances).
細い: thin/slender for long or cylindrical things (pencils, fingers, strings), or a person’s build. So an entrance or hallway is 狭い, not 細い.

What’s the difference between 広い and 大きい?

広い: wide/spacious (focus on area or breadth).
大きい: big/large in overall size or scale. Rooms, roads, spaces are typically 広い. A building can be 大きい; a room is more naturally 広い.

Could I say 店の入口が狭いが、出口は広い?

It’s grammatical. Using subject-marking が on 入口 foregrounds it as the subject rather than a contrastive topic. For a clean A-vs-B contrast, は on both nouns is the most natural: 入口は…、出口は….

Why are there spaces in the sentence? Do Japanese normally write with spaces?

Spaces were added for learners. Standard Japanese doesn’t use spaces between words. Normally you’d write: 店の入口は狭いが、出口は広い。

What particles commonly go with 入口/出口 in other sentences?

入口で待つ (wait at the entrance)
入口に並ぶ (line up at the entrance)
入口から入る (enter through the entrance) — not 入口を入る
出口から出る (exit via the exit)
出口へ向かう (head toward the exit)

Does が always mean “but”?

No. が has two main uses:

As a particle after a noun: subject marker (雨が降っている).
As a conjunction after a predicate: but/though (狭いが、広い). Context and position tell you which it is.

Is the comma after が required?

No. It’s a stylistic pause. Both are fine:

店の入口は狭いが、出口は広い。
店の入口は狭いが出口は広い。 Writers often include the comma for readability.