The theory of General Relativity is the geometric theory of gravitation published by Albert Einstein in 1916. According to the internet, it is the current description of gravitation in modern physics.
It deals with things like the mass of objects, the speed at which they travel, how speed and mass are converted to energy, and how mass warps the fabric of space and time.
In layman’s terms, “Gravity works well in some places and especially well in others.” It works especially well in my kitchen, which is why we don’t have matching cups.
But I digress.
Today we are here to discuss relativity in regard to pronouns. In the English language, the following are the most common relative pronouns: which, that, whose, whoever, whomever, who, and whom.
They are also known as possessives and genitives. We use these words every day in casual conversation, so on the surface, they seem simple. But when we write, relative pronouns can be complicated.
Most people know that an apostrophe denotes possession (and I’m not talking demonic here) or indicates a contraction.
Things to remember:
- Who’s is the contraction of “who is” or, less commonly, “who has.”
- Whose is the possessive of “who” or (controversially and only rarely) “which.”
- Their(s) is the possessive of “they.” (They’re proud to own it, it’s theirs, and it’s not there.)
- Its is the possessive of “it,” and “it’s” is a contraction of it is. Note that there is no apostrophe in the possessive form for both they and it. We will get to that later.
 Grammar-Monster says:
“Possessive adjectives and possessive personal pronouns are forms of the genitive case.” Examples:
our carpet (our – a genitive form of we)
Can I use yours? (yours – a genitive form of you) 
Who, whose, whom?
When referring to living beings, whose denotes possession and who’s is a contraction that refers to existence: who is.
 What about whom? Merriam-Webster says: Who performs the action of a verb (e.g. “Who sent us this gift?”), while whom receives the action (“We got this gift from whom?”). In grammar terms, that makes who a subject, and whom an object. When following a preposition, whom is the preferred choice (“To whom should we address our thank you note?”). 
Merriam-Webster also says the times are changing, and no one really cares except grammar nerds.
So now we have some idea of “whose” vs. “who’s” and “who” vs. “whom.”
But what about “It?” Here, we are dealing with possession by the inanimate. We don’t need an exorcist, although a good maid service would resolve a great deal here at Casa del Jasperson. But in this case, we are referencing something owned by the inanimate:
I scratched myself on its surface.
Its … it’s … which is what and when to use it? The trouble is found in the apostrophe.
In probably 99% of English words, an apostrophe indicates possession, but it also signifies a contraction.
Both it and they are frequently part of contracted words (it is = it’s, they are = they’re). So, two hundred years ago, linguists chose to eliminate the apostrophe in the possessive form in the (vain) hope of ending confusion.
- It’s is the contraction of “it is”and sometimes “it has.”
- Its denotes possession: It owns it.
 According to Dictionary.com:
Way back when in English, we used his for the possessive form of it. (That wasn’t perplexing at all.)
The use of its for the possessive form of it takes off in the 1500s.
After, we did commonly write it’s to show possession for it, but that became nonstandard in the 1800s, probably due to the influence of pronouns like yours, hers, etc. 
I love how our ancestors assumed inanimate objects were male. I took a hammer to the wall and dented his surface. The males I’m acquainted with resent being compared to inanimate objects, so we never refer to Uncle Jim as a bump on a log, to his face.
That and which are two commonly misused words. Most times, we don’t need the word that, but before you eliminate every instance, please look at each case where it is used.
Don’t gut your prose just because some online guru tells you ‘that’ is an unnecessary pronoun. Sometimes, “that” is the only word for a given situation. If you remove every instance of the word “that” you’ll end up with a mess on your hands.
Something you need to know: “that” and “which” are not interchangeable so you can’t just use a global search to change every instance of “that” to “which.”
“That” is a pronoun used to identify a specific person or thing observed by the speaker. It is a determiner, an adverb, and a conjunction.
- “That’s his dog on the curb.” (Identifier)
- “Look at that red car.” (Determiner)
- “I wouldn’t go that far.” (Adverb)
- “She claimed that she was married.” (Conjunction)
In the case of number 4, the sentence would be stronger without it. Most of the time, the prose is made stronger when the word “that” is cut and not replaced with anything. I say most, but not all the time.
There are cases where only “that” will suffice. When do we use the word “that?” We use it when we have something called a ‘Restrictive Clause,’ the part of a sentence that you can’t get rid of because it specifically restricts some other part of the sentence. We watched the stars that gleamed red and ignored those that shone white. They watched specific stars and ignored others. Sometimes you can’t get rid of that, because the phrasing would be too awkward without it.
“Which” is a pronoun asking for information. It specifies one or more people (or things) from a particular set, and it is also a determiner:
- “Which are the best diapers for newborns?” (Pronoun)
- “I’m looking at a house which is for sale on Black Lake.” (Determiner)
Go lightly with “which” and “that,” but use them when required.
The same common-sense approach goes for “very.” I seldom need to use it, but I do when required. However, some people employ it too frequently, and it’s rarely needed, fluffing up the word count.
Use common sense. Don’t run amok in your manuscript and cut every relative pronoun.
Examine each instance and try to see why the members of your writing group are pointing it out. Cut it or leave it in based on whether the phrasing would be awkward without it.
Credits and Attributions:
 GrammarMonster.com, What Is the Genitive Case? http://www.grammar-monster.com/glossary/genitive_case.htm, accessed April 12, 2022.
 How to Use ‘Who’ vs. ‘Whom © 2022 Merriam-Webster, Incorporated How to Use Who vs. Whom | Merriam-Webster, accessed April 12, 2022.
 Dictionary.com, What is the difference between its and it’s? What Is The Difference Between “It’s” And “Its”? (dictionary.com), accessed April 12, 2022.