Semantics and structural types of pronoun

First person: I conducted an experiment on seedling growth under various conditions.
Second person: You will see that the results of my experiment provided support for growing seedlings in dark conditions.
Third person: It was found that seedling growth was significantly greater in the dark than in the light.

Which to use
First (I) or Third (it)
How do you decide whether to write in the first person, the second person, or the third person? In general the approach you choose depends on the nature of the assignment, and on your department:
Nature of the assignment – usually by default you will write an academic assignment in the third person. The main exception to this is when writing reflectively, in which case you are relating your own thoughts and experiences, and first person is more appropriate.
Discipline – most disciplines, particularly the sciences and social sciences require you to write in the third person. Some areas of the humanities require first person, but this may depend on the nature of the assignment. If in doubt refer to your module handbooks and speak to your tutors.
Second (You)
The second person (e.g. “you”) is the least commonly used form in academic writing, and generally addresses the reader or audience directly. It is considered a bit chatty and as a consequence not normally used in academic writing. One example of where it may be appropriate to use the second person is in the delivery of presentations where you may wish to address your audience directly.
We
'We' should only be used if you have co-written a paper. We suggest that... would then be perfectly acceptable. Students often fall into the trap of using 'we' to mean all human kind, or all researchers, or all historians etc. This should also be avoided as you are making the reader guess who you are referring to. It is better to use the actual noun rather than the pronoun in this case. Alternatively you can switch to the third person i.e.

Wrong:	We have been able to make connections between corvid and ape intelligence. For example...
Better:	Some researchers have been able to make connections between corvid and ape intelligence. For example...
Or:	It is possible to make connections between corvid and ape intelligence. For example...

They/Their
There is a lot of debate about whether you should be able to use they/their as gender-neutral single third person pronouns as in the following sentences:

Each child was able to make the choice they believed to be correct.

A nurse should be able to make appropriate decisions about the care of their patient.

Strictly speaking, these sentences are grammatically incorrect as they and their are plural pronouns. One way to solve the problem is by switching to the plural noun in the earlier part of the sentence:

Nurses should be able to make appropriate decisions about the care of their patients.

Where this is not appropriate you could use the more correct his/her or he/she (or even (s)he) which also avoids the problem:

Each child was able to make the choice (s)he believed to be correct.

Language is changing however and so is society. Many people no longer associate themselves with a specific gender which can cause grammatical issues when referring to them. They/their as gender neutral single third person pronouns is common in our spoken language and is becoming more acceptable in written language. As with all things, check with your tutor to see if he/she/they (!) have a personal preference if you are unsure.
AD
Pronouns: personal (I, me, you, him, it, they, etc.)
Grammar > Nouns, pronouns and determiners > Pronouns > Pronouns: personal (I, me, you, him, it, they, etc.)
from English Grammar Today
We use personal pronouns in place of noun phrases. We often use them to refer back to people and things that we have already identified (underlined):
Peter complained to the chef about the meal. She wasn’t very helpful so he spoke to the manager. (she = the chef, he = Peter)
A:
Where’s the knife? I can’t find it.
B:
It’s in the drawer. (it = the knife)
Personal pronouns show person and number. He, she, him and her show gender. They have different subject and object forms (except you, it and one which have only one form):

subject	object	number	gender	person
I	me	singular		first
you	you	singular or plural		second
he	him	singular	masculine	third
she	her	singular	feminine	third
it	it	singular		third
we	us	plural		first
they	them	plural		third
one	one	generic		third

Subject and object pronouns
Personal subject pronouns act as the subject of a clause. We use them before a verb to show who is doing the verb. We do not usually leave out the pronoun:
She loves playing basketball.
Not: … loves playing basketball.
They don’t finish the lesson until four o’clock.
It’s getting late.
We use personal object pronouns in all other positions, such as after the verb or after a preposition:
Paula’s coming to visit us in September. (us = object)
Thanks again for everything you did for me. (for me = prepositional phrase)
We also use personal object pronouns as complements of the verb be:
That’s him. That’s the man I was talking about. (him = complement of be)
We can use some object pronouns (me, him, her, us and them) as short answers, particularly in informal speaking:
A:
Who ate all the biscuits?
B:
Me. (or more formally: I did.)
I, me
We use I and me to refer to the speaker or writer. I is the subject form and me is the object form:
I can’t come on Friday. I’m working.
I am writing to apply for the position of …
Helen asked me to get some milk.
It’s me. Can you open the door? I haven’t got my key. (It is I. is not often used. It is very formal.)
Spoken English:
We sometimes hear me used as a subject in informal speaking after another subject + and:
My friends and me went on holiday to a little town on the south coast. (or Me and my friends went on holiday …; My friends and I went … is considered to be more correct.)
We sometimes use us to refer to me in informal speaking:
Pass us an orange, will you?
You
We use you to refer to the listener or reader. It is both the subject and the object form. You can refer to one person or more than one person. It is usually clear from the context whether you is singular or plural:
Paul, do you need any help? (refers to one person, Paul)
[coach to team]
The match starts at 10.30. I need you to be here at 10. (refers to a group of people)
We sometimes use you all to address everyone in a group:
What would you all like to eat?
In informal contexts, we also use you to refer to people in general, not someone specific:
You get a pension if you’re a man over the age of 65 or a woman over 60.
He, him; she, her
He, him, she and her are singular third person pronouns. He and him are the masculine forms. She and her are the feminine forms:
A:
Have you seen Johnny Roberts recently?
B:
Yes I saw him in town last week. He’s looking really well.
She didn’t like the way he spoke to her.
Traditionally, he and him were used to refer to both genders in formal writing:
If anyone has any evidence to oppose this view, let him inform the police immediately.
Nowadays, we often see gender neutral forms (e.g. he or she, he/she, s/he, (s)he, they and him or her, him/her, them) when we do not know if the person referred to is male or female:
The bank manager could help with your problem. He or she will probably be able to give you a loan. (or … he/she will probably be able to … or … they will probably be able to …)
Go to a hairdresser. Ask him or her to come up with a style that suits you, your hair, your lifestyle. (or … ask him/her to come up with a style … or … ask them to come up with a style …)
When you get into the building, go to the person on the desk in the reception area. They can tell you where to go. (or He or she can tell you where to go.)
See also:
One
Sexist language
It
We use it to refer to things:
My computer isn’t working. It’s crashed again. Can you have a look at it?
We use it as an empty pronoun, also known as a ‘dummy’ subject, where there is no other subject to put in the subject position, particularly when referring to the weather or time:
It’s so lovely to see you.
It’s already ten o’clock.
It’s snowing.
We usually use it to refer to countries, vehicles and machines. In some traditional styles, she was sometimes used, but this is now considered inappropriate by many people:
We spent three weeks in Malaysia. It’s a beautiful country.
Three hours after the ship sailed, it developed engine trouble. (or, more traditionally: … she developed engine trouble.)
See also:
Subjects
It
Sexist language
Dummy subjects
We, us
We use we and us to refer to different groups of people, but always including the speaker. We and us can refer to the speaker + the listener, or the speaker + other people but not the listener, or people in general including the speaker:
We could go and see a film tonight. What do you think? (we = speaker + listener)
Gerald asked us if we’d drive to London and get you. (us/we = speaker + others but not listener you)
Changing diet, rather than dieting, is a healthier alternative. There are changes we should all make. (we = speaker + listener + all other people)
They, them
We use they and them to refer to specific groups of people, things and animals:
The kids are getting on my nerves. They’re making so much noise. Can you tell them to be quiet? I’m trying to work.
A:
Have you seen my keys? I never remember where I’ve left them.
B:
They’re by the front door.
We also use they and them to refer to institutions or authorities, and groups of people in general:
I heard they’re going to publish a new edition of ‘War and Peace’.
They’re opening the new motorway tomorrow.
See also:
Pronouns
One
Conclusion
The pronoun ‘you’ is the second person pronoun that can be used in both the singular and plural form.
Example 1: You are from Columbia, right?
In the above sentence, ‘you’ can be a male or a female.
Example 2: Did you do your assignments?
In the above example, ‘you’ can refer to a singular or plural noun and also a group of male and female students.

‘They’ and ‘Them’

The third person pronouns ’they’ and ‘them’ can be used when the gender of a third person singular pronoun is neutral or cannot be determined.
Example 1: Everyone has to make sure if he/she has his/her ID cards before he/she goes into the exam hall.
When you have to write for the general public, people use he/she or him/her. It can also be written in the following manner.
Everyone has to make sure if they have their ID cards before they go into the exam hall.