Indo-European languages have two distinct features:
1. Cognates (words with similar structure and meaning, sharing a common linguistic ancestor)
Some examples:
| English | Dutch | German | Norwegian | Lithuanian | Celtic |
| mother | moeder | mutter | mor | mater | mathair |
| three | drie | drei | tre | tri | tri |
| me | mij | mich | meg | manen | me |
| brother | broeder | bruder | bror | brothar | brathair |
| Latin | Italian | Spanish | French | Sanskrit | Greek |
| mater | madre | madre | mere | matar | meter |
| tres | tre | tres | trois | tri | treis |
| me | me | me | moi | me | me |
| frater | fra | hermano | frere | bhrator | phrater |
2. Inflections (an alteration in or addition to a form of a word to indicate such things as case,
gender, number, mood, and tense)
Some examples: sing, sang, sung
walk, walked
I, me; we, us
girl, girls
talk, talked
English: Yes, mother, I have three.
Icelandic: Ja, modir, eh hefi thrja.
Swedish: Ja, moder, jag har tre.
Danish: Ja, mor, jeg hav tre.
Norwegian: Ja, mor, jeg har tre.
German: Ja, mutter, ich habe drei.
Dutch: Ja, moeder, ik heb drie.
Flemish: Ja, moeder, ik heb drie.
French: Oui, mere, j'en ai trois.
Spanish: Si, madre, yo tengo tres.
Portuguese: Sim, mae, tenho tres.
Italian: Si, madre, ce h'ko tre.
Romanian: Da, mama mea, eu am trei.
Czeck: Ano, matko, mam tri.
Polish: Tak, matko, mam trzy.
Russian: Da, mat u men'a tri.
Bulgarian: Da, maika, imom tri.
Compare these to the non-IE Finnish: Kyllä, äiti, minulla on kolme.