Why are Russian numerals so complicated?

In Russian, we use three forms of nouns after numerals depending on the last number:

1 year – 1 год

2, 3 or 4 years – 2, 3 или 4 года

5, 6, 7, 8 or 9 years – 5, 6, 7, 8 или 9 лет

These are the remains of the ancient Slavic in which, along with singular and plural forms, the intermediate “little plural” form existed. It was important for them to mention that 2, 3 or 4 are more than 1 but still are small numbers. Grammatically, the noun года is the Genitive singular of the noun год.

So, why do we use лет when it comes to 5 years and more? It should be mentioned that лет is the Genitive plural of the noun лето (Summer). It is because our ancestors counted years by the warmest season of the year – Summer.

The same happens to other nouns we use with numerals:

Dress – платье

1 dress – 1 платье (Nominative singular)

2, 3 or 4 dresses – 2, 3 или 4 платья (Genitive singular)

5, 6, 7, 8 or 9 dresses – 5, 6, 7, 8 или 9 платьев (Genitive plural)

Glass – стакан

1 glass- 1 стакан (Nominative singular)

2, 3 or 4 glasses – 2, 3 или 4 стакана (Genitive singular)

5, 6, 7, 8 or 9 glasses – 5, 6, 7, 8 или 9 стаканов (Genitive plural)

Girl – девушка

1 girl – 1 девушка (Nominative singular)

2, 3 or 4 girls – 2, 3 или 4 девушки (Genitive singular)

5, 6, 7, 8 or 9 girls – 5, 6, 7, 8 или 9 девушек (Genitive plural)

etc.