под - prefix тверд - firm ить - suffix подтвердить - Agree or Prove or Assure You can say: Этот камень тверд - This means that the stone is hard. Or you can say: я подтверждаю (под+тверж/д+даю) свое намерение учить язык - I confirm my intention to learn the language Or: этот человек твердо (уверенно) стоит на ногах - this man is firmly on his feet. there is a word: отвердеть (о+тверд+еть) - it means - to become solid

под - It's mean under, below and nothing else. твёрдый - You are right, hard and solid. ить - Makes verb from adjective. For example: твёрдый (adjective) - твердить (verb, means to repeat), мягкий (soft) - смягчить (to make softer), мокрый (wet) - мочить (wet like verb). подтвердить - confirm, to declare about your position / decision firmly.

It is a calque form Latin or Greek. It is "confirm". literally it is "underfirm". Also: "твердить" - "to keep insisting on..", "to keep repeating" "утверждать" - to state, "утверждение" - an assertion. another meaning of "утверждать" is just to make somethign firm, to put something firmly on the ground.

Morphology and etymology are not the same thing exactly. The imperfective verb "подтверждать" derives from the perfective verb "подтвердить" (the process is called "imperfectivation") by means of changing the suffix -и- to -а-. In its turn, the perfective "подтвердить" derives from the imperfective "твердить" by means of adding the prefix под- (this on the contrary is called "perfectivation"). So you have: подтверждать < подтвердить < под+твердить The verb твердить means 'to (constantly) repeat the same thing". The prefix под- has multiple meanings and can form verbs, noun, adjectives and adverbs. In this case, it means an action of copying/following someone's action ( https://en.wiktionary.org/wiki/%D0%BF%D0%BE%D0%B4-) Thus, the pair подтверждать/подтвердить means to confirm/affirm/reaffirm, i.e. to assert something that has already been established, said etc

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