API – How to determine non-entity words in the English text such as: "is", "the", "on", "rather", "both", etc.?

How can I determine words in the English text such as:

the, one, one, this, that, these, my, your, his, his, his, our, their, their, them, a little, many, many, many, many, many, enough, all, the two, half, neither, nor one, nor the other, neither, another such, what rather, quite, etc.

  • I do not even know how these words call.
  • Would there be a list somewhere we could use?
  • Is there an API that we can use to determine these words?