硬い【かたい】 (adj-i) (1) hard; solid; tough; (2) stiff; tight; wooden; unpolished (e.g. writing); (3) strong; firm (not viscous or easily moved); (4) safe; steady; honest; steadfast; (5) obstinate; stubborn; (6) bookish; formal; stuffy; (P).　 硬い石【かたいいし】 (n) hard stone. 硬い表情【かたいひょうじょう】 (n) stiff expression. 硬い文章【かたいぶんしょう】 (n) stiff style. 堅い【かたい】 (adj-i) (1) hard; solid; tough; (2) stiff; tight; wooden; unpolished (e.g. writing); (3) strong; firm (not viscous or easily moved); (4) safe; steady; honest; steadfast; (5) obstinate; stubborn; (6) bookish; formal; stuffy; (P).　 堅い言葉【かたいことば】 (n) stiff speech. 堅い材木【かたいざいもく】 (n) hard lumber. 堅い女【かたいおんな】 (n) chaste woman. 固い【かたい】 (adj-i) (1) hard; solid; tough; (2) stiff; tight; wooden; unpolished (e.g. writing); (3) strong; firm (not viscous or easily moved); (4) safe; steady; honest; steadfast; (5) obstinate; stubborn; (6) bookish; formal; stuffy; (P). 固い握り【かたいにぎり】 (n) tight grip. 固い約束【かたいやくそく】 (n) solemn promise. 固い話【かたいはなし】 (n) serious topic (of conversation). These 3 Katai words are similar in menanings. When you talk, they sound the same.

usually, you can write like this, 硬い石（いし）、硬い文章（ぶんしょう）、硬い表情（ひょうじょう）、堅い木（き）、など。堅い and 固いare usually used with things like belief, determination, defense, foundation, etc. and as a matter of fact, japanese people sometimes connect 固い and 堅い with the same subjects. so if you're not sure, why not just use かたい？quite a few japanese people are doing like this when they write!

Hi AJ, try to copy/paste into the Japanese to English dictionary containing 174285 references. Search by romaji, kana or kanji. www.online-dictionary.biz/japanese/english/