# How does counting change the suffix of a word?

When counting things, as in 1, 2, 3, 4, ... what suffix is applied to the end of the words? For instance:

There is 1 dog, but 2 cats.

There are 3 planes available today.

The first 4 doors are locked, but the 5th door is not.

When counting there are three plural forms when the object being counted is the subject of the sentence. Let n represent a number.

• the last (units) digit of n is 1 but the last two digits are not 11: use nominative singular

один кот, двадцать один кот, сорок один кот, тысяча один кот...

• the last (units) digit of n is 2, 3, or 4 but the last two digits are not 12, 13, 14: use genitive singular

два кота, три кота, четыре кота, двадцать два кота, тридцать три кота, сорок четыре кота...

• all other cases: the last two digits are 11, 12, ..., 19 or the last digit ends in 5 or higher or ends in 0. Use genitive plural.

пять котов, десять котов, семнадцать котов, двадцать котов, тысяча одиннадцать котов

• If the object being counted is not the subject, then the number get declined along with the counted object in the same case, using the counted object in plural if the number is more than 1, e.g., he has two friends = у него есть два друга (gen. singular for друг), he was talking with two friends = он разговаривал с двумя друзьями (instrumental for два and instrumental plural for друг).
– KCd
May 25 '14 at 2:04
• Feminine numeration is also interesting :) Одна кошка. две кошки,... пять кошек,... двадцать одна кошка,... May 26 '14 at 1:14