The grammatical person is a contextual reference to a person in an event. The most familiar types of references are first person:
“I am reading this.”
and third person:
“He read it.”
Most literature is written in this form with a couple of exceptions, such a Choose Your Own Adventure books:
“You read the book.”
First person is limited to “I”, Second is only “you”. Third contains “he, she, it, they we, etc.”
Are there other types of grammatical persons? Oddly, yes. Fourth person is a “obviative” reference to a third person who is far removed from the activity.
“One should know…”
These are difficult to phrase in English and are tiresome to read and write. If the subject is so far removed from the event, why bother to mention it? In other languages, there is fifth person where the subject is even more removed from the action. These languages (Potawatomi for example) mark the fourth and fifth person as obviative
So does it end with fifth person? It should, because this is another edition Just Five Things. But grammatical person is a special case.
There is the Zero person in some languages such as Finnish. The Zero person is a non existent subject of a very. Literally, the subject is “null”. English does not work well with this form. Construction of such sentences in English are usually rendered as “One will…”, “One has…” and so on. A sentence without a subject would sound like a command in English. The concept sounds mind bending to English speakers, but in languages like Finnish, even children can easily use the Zero person.
Now you know.