I have been trying to figure out how words are categorized into parts of speech. The way I understand it, words can only be included into various parts of speech depending on their meaning and usage in a sentence. So It's not possible to figure out what category a word falls into just looking at the word rather you have to put them into a sentence. Words like act, laugh, attack etc. can be both verb and noun at the same time inspected in isolation.
But it turns out that even analysing a sentence cannot determine what category they fall into. See the example John Lawler gives in this related question: https://english.stackexchange.com/questions/388099/how-many-parts-of-speech-can-a-word-be-at-the-same-time
- I was exhausted.
- I was exhausted and the bed was soft; we suited each other well.
- I was exhausted by the irritable conversation and left early.
"But that's not "in the same sentence". In the first sentence, there's just no way to know what the speaker intends about POS; it could be either one. And there's no way to know if one speaker might feel it was an adjective, but another speaker might think it was a participle. Or the same speaker might do both, to the same sentence, on different occasions."
Here the word exhausted is both a participal adjective and a verb at the same time. But can't you say that the adjective("exhausted") was formed from the verb exhaust and so the word here is "primarily" a verb which can act as an adjective. Wouldn't this allow us to put the word "exhaust" and "exhausted" into a primarily verb category? This is in some sense a word formation analysis to determine what the essence/category of a word is.
But one another sentence where this technique doesn't happen to work is:
"It is light."
You can see that "light" works here both as a noun(as in "bright light") and an adjective(as in: "That bag is light") but I can't seem to find a primary meaning to the word which I think would require a historical analysis of the word formation to categorise. I am not even sure if this a proper technique to categorise these words and it feelslike I am shoehorning words here into exclusive categories.
In short: Are parts of speech really sharply defined exclusive categories where a single word (when analysed within a sentence) falls into a single group or are they heterogeneous categories where words get shared within parts of speech categorizations?
Update: Adding some pointers if someone stumbles on this question in the future.
On further inquiry, I came to know that this problem is documented as Intersective Gradience: https://www.google.co.in/books/edition/The_Oxford_Dictionary_of_English_Grammar/9zVOCgAAQBAJ?hl=en&gbpv=1&pg=PA184&printsec=frontcover&bsq=Gradience
Also see Bas Aarts' Syntactic Gradience for a thorough take on the issue, By the end of his book there is a section on true hybridity which is approachable and could give you a clearer picture on the issue: https://www.google.co.in/books/edition/_/pN5zQgAACAAJ?hl=en&sa=X&ved=2ahUKEwizjpyDlcrtAhVSyzgGHc-FDvMQre8FMBF6BAgLEAM
A brief intro to Gradience: https://www.thoughtco.com/gradience-language-term-1690906