title_body: Languages where the part of speech of a root is "fixed"? By way of introduction, this question is about a quirk of Esperanto, but there is a general conlang question at the end, I promise.
  
  In Esperanto, every root has a natural grammatical part of speech, much like how nouns have a grammatical "gender" (or noun category) in many other languages.
  
  For example, "ŝoveli" means "to shovel". It is naturally a verb. The same root with a noun ending, "ŝovelo", does not mean "a shovel". Rather, it is the noun-of-the-verb, that is, it refers to the act of shovelling. To refer to a shovel, you have to say that it's the tool of the act of shovelling, that is, "ŝovelilo".
  
  Similarly, "humana" means "humane". It is naturally an adjective. The same root with a noun ending, "humano", does not mean "human", it is the noun-of-the-adjective, that is, "humaneness".
  
  This was an interesting design choice, and one that's puzzled me. For an Esperanto speaker, this is something you have to learn about every root, like noun classes in many IE languages.
  
  Are there any analogues to this in natural languages, or is this a device that has been used in other conlangs?
upvoted_answer: This is pretty common in natural languages. Think about English words -- most of them have an inherent part of speech and require derivational affixes to change that. "Anger" is inherently a noun and requires "-y" to become an adjective, whereas "excite" is inherently a verb and requires "-ment" to become a noun or "-ed" or "-ing" to become an adjective. This sort of thing is incredibly normal in natlangs -- the reason it seems a bit abnormal in Esperanto is that Esperanto derivation is far more productive than even derivation-heavy natlangs, leading to irregularities in these sorts of changes being much more noticeable.
  
  Also, as an aside, because "human-" is inherently adjectival, you would not say "humano" to mean "humane-ness", but "humaneco" (source). Adding the "-eco" suffix, meaning "the quality of" or something to that effect, is necessary for adjectival Esperanto roots. This is the very reason why Esperanto roots are said to have inherent part of speech, and it's a large part of why the "-eco" suffix exists in the first place.