An object is "fest" when it is so tightly attached to something else that it cannot be moved. There are numerous verbs that describe how something is made "fest": festbinden, festkleben, festklopfen, festschrauben ... The opposite of "fest" is "locker" (loose). On the other hand, we use the adjective "hart" when the surface of an object cannot be penetrated. Examples for materials an objects that are "hart" are: Diamant, Stein, Stahl, .. There is also the adjective "steinhart", meaning "hard as stone". The opposite of "hart" is "weich" (soft).

These words are very similar to each other. Considering the structure or the surface of an object, you can use eather hart or fest. example: Das Holz ist hart. = Das Holz ist fest. Sometimes, it's a matter of feeling which one sounds better. Native speakers won't blame you for choosing the ,,wrong" word in a special context. However, ,,fest" can also be used as a synonym for ,,stark" (strong): - jemand glaubt fest an etwas. (somebody strongly believes in sth.) - jemand hat einen festen Willen - jemand leistet festen Widerstand ,,hart" can be used as a synonym for ,,schwierig" (tough): - harte Zeiten - eine harte Aufgabe etc. I hope that helped a bit!

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