It's in Capital Letter but not a Proper Noun

why?

if the word does

not name
a person, place, thing or idea
 

it is

not

a

proper noun

so even the first word of a sentence

is not a proper noun, it's still written 

in capital letter

like in a
song
[Heal the World,]

movie
[So Close],

poem
[Mi Ultimo Adios],

book
[The Adventures of Huckleberry Finn]

...et cetera...

but then again,

it's a rule to write it that way though

it's not always a proper noun

and
it's a pronoun.

noun and pronoun are two different things!

something in your mind
that uses capital letter???

hmm,

well, since most of the acronyms
are the initials of the actual names of
organizations, companies, bands, teams, groups
then it is a proper noun

World Health Organization - WHO

but there are acronym
that will remain written in lowercase
because it is not specific name
but just an initials of words
to define a new thing like

 

and most of us
considered that "laser" is just a word
we use for that beaming light
that scan or cuts in precision

btw, laser is a noun.
oppsss!
btw is a shortened "by the way"

about abbreviation,
well it depends on where it will be used.
 

how come?

well, it will only be in capital letter

when it is use as part of any
specific - actual - particular
name of person, place, thing or idea.

let me give you some example:

street is abbreviated as st.

and yes, it is a common noun

that's why it is written in lowercase

it will become a proper noun
when you point out
the name of a particular street like

 

and this is also applies in

avenue [Avenida 9 de Julio Ave.],

boulevard [Champs-Elysees Blvd.],
mountain [Mt. Mayon Volcano],

drive [Chapman's Peak Dr.],

highway [Karakoram Hwy.],

road [Atlantic Rd.]

the abbreviation of direction

are always in capital letter

north - N

east - E

west - W

south - S

this also goes in addressing a person

doctor Dr. Seuss

sergeant Sgt. Pepper

colonel Col. Lone

fyi
[for your information]

there is no abbreviation for teacher
and it not used as a title.

surprise?!?

that's why we address a teacher
by Mr., Mrs., or Miss then
followed by their family name or
unless they preferred 

Sir and Ma'am 

or just like Prof. Utonium.

but of course
every rule has an exemption!!!

it's a good feeling to be called
"Teacher Maven"
by the young learners

...again...

it's just fine for a kid to that
but eventually it must be corrected.

...

a teacher teaches other professions
that why they don't deserve to be abbreviated
after all it's a noble profession!
...just a passing thought of mine...