固い vs 硬い vs 堅い
JLPT N4 vocabulary · what is the difference?
All three are read かたい and all mean some kind of "hard". The reliable split is: 硬い for a material that resists being dented or bent, and for a stiff manner or style; 堅い for things that are solid, sturdy and dependable, like a steady job or someone who keeps a secret; 固い for things fixed tight or unyielding, like a stuck lid, a firm promise or a stubborn head. The boundaries genuinely overlap and dictionaries disagree, so kana かたい is common and never wrong.
When to use each
固い
かたい
Use 固い when something is fastened tight, set firm, or will not budge — a stuck lid, frozen ground, a firm promise, a stubborn mind, a fixed resolve. The feeling it opposes is loose rather than soft.
固い約束をしました。
かたいやくそくをしました。
We made a firm promise.
父は頭が固いです。
ちちはあたまがかたいです。
My father is inflexible.
硬い
かたい
Use 硬い for the physical hardness of a substance — the opposite of 柔らかい — and for stiffness in a figurative sense: a tense expression, a dry and formal writing style, a nervous performance.
この石はとても硬いです。
このいしはとてもかたいです。
This stone is very hard.
緊張して表情が硬いですね。
きんちょうしてひょうじょうがかたいですね。
You look tense — your expression is stiff.
堅い
かたい
Use 堅い for solidity you can rely on: sturdy construction, a secure job, a cautious and sober person, a safe bet. It carries approval, and what it opposes is flimsy or unreliable.
彼は口が堅いです。
かれはくちがかたいです。
He can keep a secret.
堅い仕事に就きたいです。
かたいしごとにつきたいです。
I want a steady, secure job.
Sentences where only one works
ダイヤモンドは世界で一番硬い。
ダイヤモンドはせかいでいちばんかたい。
Diamond is the hardest thing in the world.
Hardness as a property of the material itself is squarely 硬い; this is the one use nobody disputes.
ふたが固くて開きません。
ふたがかたくてあきません。
The lid is stuck and won't open.
Nothing here is about a substance being hard — the lid is fixed tight, which is 固い.
合格は堅いでしょう。
ごうかくはかたいでしょう。
Passing is a safe bet.
Solid, dependable, sure to hold — that is the 堅い sense, and the other two kanji do not carry it.
このパンはかたいです。
このパンはかたいです。
This bread is hard.
Food is exactly where the kanji overlap: 硬い is the more standard choice for texture, but 固い is widely used, and many publishers simply write kana. This is a real ambiguity, not a rule you have missed.
Common mistakes
彼は口が硬い。
彼は口が堅い。
口が堅い is a set phrase written with 堅い. Another kanji is read the same aloud but looks wrong in print.
決意が硬い。
決意が固い。
Resolve is fixed rather than physically hard, so 固い — the same logic as 固く信じる and 団結が固い.
硬い木の机（丈夫でしっかりした机という意味で）
堅い木の机
If you mean the timber resists scratching, 硬い is right; if you mean the desk is solidly built and will last, that is 堅い. Learners reach for 硬い for both.
Frequently asked questions
Which one should I write if I'm not sure?
Write かたい in kana. Japanese newspapers and textbooks do this routinely for exactly this word, and no reader will think it is a mistake. If you must pick a kanji, 硬い for physical hardness and 固い for everything else will be right most of the time.
Is 硬い or 固い correct for hard bread?
Both appear in print, and dictionaries do not agree. 硬い fits better if you mean the texture is tough to bite; 固い suggests it has dried out and gone stiff. Nobody will misunderstand you either way.
Do I need to write these apart for the JLPT?
No. The JLPT never asks you to produce kanji, so you only need to recognise the three and know that they all read かたい. The distinction matters when you write Japanese yourself.