The Turkish language has eight vowels. We call four of them "ince" and four of them "kalın".

ince : thin, slim (for the soft vowels)

kalın : thick (for the hard vowels)

yumuşak : soft

sert : hard

For the learners, it may be better to call "soft" and "hard".

The major vowel harmony that is one of the most essential situations of Turkish grammar is very important in aspect of deciding on a suffix. One usually adds the suffixes according to the major and minor vowel harmonies.

The major vowel harmony is summarily this:

Examplifying by teaching how to express the plurality:

-LER/-LAR

Summarily, if you want to use a noun in plural form, you add to it -LER or -LAR according to the major vowel harmony. Just this. By the way, these plural suffixes has no form else. Just -LER or -LAR.

bilgi : 1knowledge, 2information

The last vowel is İ. It´s a soft vowel. Hence -LER, because E is a soft vowel.

Kitapta ülkemizin yakın tarihi hakkında önemli bilgiler anlatılmış. (In the book, one has told about important informations about the recent history of our country.)

kitap : book ; ülke : country ; yakın : near ; tarih : 1date, 2history ; ... hakkında : about ... ; önemli : important, significant ; anlatmak : to tell 

okul : school

The last vowel is U. It´s a hard vowel. Therefore the suffix must -LAR, because A is hard.

Türkiye´de okullar genellikle Haziran´da kapanır. (The schools usually start the vacation in Turkey in June.)

genellikle : usually ; Haziran : June ; kapanmak : 1to be closed, to get closed, 2to overcloud, 3to scar over

çiçek : flower

The last vowel is E. It is SOFT. The suffix must include

Çiçeklerden biri sarıydı. (One of the flowers was yellow.)

sarı : yellow

gül : rose

It already has just one vowel, and it is soft. The suffix must soft vowel, too.

Türk edebiyatındaki şiirlerde güllerden sık sık bahsedilir. (One talks about the roses in the poems that in Turkish literature.)

şiir + ler ---------> şiirler (poems)

edebiyat : literature ; şiir : poem ; sık sık : often, frequently ; bahsetmek : to talk about

çorap : sock

The last vowel is A, that´s to say a HARD vowel. Therefore it must be "-LAR", not "-LER" because the hard one is "-LAR".

Çoraplarımı bulamıyorum. (I cannot find my socks.)

bulmak : to find

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Yıllar geçtikçe teknoloji daha fazla gelişiyor. (As long as the years elapse, the technology develops much more.)

yıl, sene : year

yıl lar ---------------> yıllar (years)

I is a hard vowel. -lar is ideal one because A is hard.

geçmek : 1to pass, 2to exceed, 3to elapse, 4to be valid, 5....

gelişmek : to develop

İnsanlık tarihinin büyük bir kısmı savaşlarla dolu. (A big part of the history of humankind is full of battles.)

savaş : war, battle

savaş lar ------------> savaşlar (wars, battles)

savaş lar la----------> savaşlarla (with the wars, with the battles)

A is hard. -lar must be brought, A is hard.

insan : human

insanlık : humankind

tarih : 1history, 2date

büyük : big

kısım : part

dolu : 1full, 2hail

O klasör inşallah silinmemiştir, ödevimle ilgili tüm belgeler o klasördeydi. (I wish that folder hasn´t been deleted, all the documents about my homework was in that folder.)

belge : document

belge ler ------------> belgeler (documents)

E is soft. -ler must come.

klasör : folder

inşallah : religional expression of "I wish, "I hope".

ödev : homework

tüm : 1all, all of, 2whole

Çiğnenmemesi gereken en önemli kurallardan birinden bahsetmek istiyorum. (I want to talk about one of the rules that one had better not breach.)

kural : rule

kural lar ------------->kurallar (rules)

A is hard. -lar must come.

çiğnemek : 1to chew, to masticate 2to trample, 3to breach (synonym: ihlâl etmek)

önemli : important

bahsetmek : (uses with ablative case) : to talk about

istemek : to want

Dükkanları bugün erken kapattılar. (They closed the shops today early.)

dükkan : shop

bugün : today

erken : early

kapatmak : to close

PLURALITY IN USAGE OF THE NUMBERS

How to express the internumbers?

A few examples can be enough to tell:

12----------->10+2--------->on+iki--------->on iki

25----------->20+5--------->yirmi+beş------>yirmi beş

33----------->30+3--------->otuz+üç------->otuz üç

49----------->40+9--------->kırk+dokuz----->kırk dokuz

97----------->90+7--------->doksan+yedi--->doksan yedi

110---------->100+10------->yüz+on-------->yüz on

182---------->100+80+2---->yüz+seksen+iki->yüz seksen iki

500---------->5x100-------->beşxyüz------->beş yüz

677---------->6x100+70+7-->altı yüz yetmiş yedi

3888--------->3x1000+8x100+80+8---------->üç bin sekiz yüz seksen sekiz

4200455----->4x1000000+200x1000+4x100+50+5-->dört milyon iki yüz bin dört yüz elli beş

If the number is more than 1, no need to add plural suffix to the noun because 2 and other numbers already expresses the plural quantity.

Dün yalnızca üç dersim vardı. (I had only three lessons yesterday.)

üç ders (three lessons)

üç dersler

dün : yesterday ; yalnızca : only, just ; ders : lesson

Yirmi yedi yıl çalıştıktan sonra emekli oldu. (He retired after he had worked for twenty seven years.)

yirmi yedi yıl (twenty seven years)

yirmi yedi yıllar

çalışmak : to work ; emekli : retired ; emekli olmak : to retire (purely: to become retired)

Birkaç ay burada kalacağız. (We will stay here for a few months.)

birkaç ay (a few months)

birkaç aylar

ay : 1month, 2moon ; burada : here [purely: in this place] ; kalmak : 1to stay, 2to remain

Yapmam gereken bazı işler var, sonra geleceğim. (I have some businesses to do, I shall come later.)

bazı işler (some businesses)

yapmak : 1to do, 2to make, 3to fulfil,

gerekmek : to be necessary, to be needed

iş : 1work, 2business, 3job

sonra : 1later, 2then, 3after

gelmek : to come

Now let´s talk also about the exceptional situations.

1) sıfat yapan -ki (the -ki which makes adjective)

balkon (balcony)

masa (table)

masa balkonda (the table is at the balcony)

balkondaki masa (the table that/which is at the balcony)

her şey (everything)

ev (house, home)

her şey evde (everything is at home)

evdeki her şey (everything which is at home)

liman (harbour)

gemi (ship)

gemiler limanda (the ships are at the harbour)

limandaki gemiler (the ships that/which are at the harbour)

yer (1place, 2floor)

halı (carpet)

beyaz (white)

beyaz halı (white carpet)

beyaz halılar yerde (the white carpets are on the floor)

yerdeki beyaz halılar (the white carpets that/which are on the floor)

yerdeki halılar (the carpets that/which are on the floor)

yerdeki halılar beyaz (the carpets that are on the floor are white)

There are some exceptional words for major vowel harmony. Even if their last vowel is hard, they take suffixes with soft vowels.

A) 

saat (1the watch, 2hour)

harf (letter)

harp (battle, war)

Kril alfabesinin harfleri göze hoş geliyor. The letters of Cyrillic alphabet are sightly. (purely: The letters of Cyrillic alphabet are coming to the eye nicely)

B) 

hâl (1case, 2situation, 3position)

ihmâl (neglection)

festival (festival)

petrol (petrol)

Kemal (a male name) (see: Mustafa Kemal Atatürk)

final (1the final, 2the final exams in the university)

meşgul (busy)

faul (fault (sport))

alkol (alchohol)

kalp (heart)

rol (role)

moral (morale)

gol (goal) [in football : score point]

"l" is softening the last vowel which is in front of it if those words are foreign origined. Thus a soft vowel is being needed so that the major vowel harmony continues. 

Bu maçta kaliteli goller izledik. (We watched goals in high quality in this match.)

O petroller çok kaliteli. (Those petrols are so qualified.)

Festivaller düzenlendi. (The festivals have been organized.)

Meşgulüm. (I´m busy)

Sınavım çok kötüydü, moralim şu an çok kötü. (My exam was too bad, I feel myself too bad now (purely: ....... , my moral is too bad now.))