Learn Hardcore Russian: Я люблю тех друзей.

In this sentence, тех друзей is in the accusative case. However, since друзья (friends) is an animate noun in the plural, Russian grammar requires that its accusative form matches the genitive plural. That’s why you see друзей instead of the nominative друзья, and correspondingly the demonstrative becomes тех (the accusative/genitive form of тот).

Why is the demonstrative pronoun тех used here instead of эти or этих?

The choice of тех comes from both case agreement and the distinction in meaning. While эти is the nominative plural form meaning these, its proper accusative form for animate nouns would be этих. In contrast, тех is the accusative (which overlaps with the genitive for animate nouns) form of тот, meaning those. The speaker uses тех to specifically refer to those friends, potentially implying a sense of distance or a defined group separate from those immediately present.

Why does друзей have the ending -ей instead of remaining друзья?

For animate plural nouns in Russian, the accusative case is expressed using the genitive form. The nominative plural друзья changes to друзей in the accusative (and genitive) because of this rule. This transformation helps signal that the noun is animate and is functioning as the direct object of the verb.