Learn Turkish: Felsefemiz, herkese bu ilkeyi benimsetmektir. - Our philosophy is to make everyone adopt this principle.

The -tir is the copula suffix, acting like the English verb 'is'. As this lesson covers, when an infinitive like benimsetmek is the predicate of a sentence (meaning 'Our philosophy is to...'), you can attach the -DIr suffix to the infinitive to complete the equation between the subject and the action.

Is the -tir at the end of the sentence absolutely necessary?

Grammatically, no. You could just say Felsefemiz ... benimsetmek and it would mean the exact same thing, which is very common in everyday speech. Adding -tir makes the statement sound more formal, definitive, or factual, which perfectly suits the tone of stating a core philosophy or goal.

Why does herkes take the dative case (herkese) here instead of the accusative?

This happens because of how causative verbs work. The base verb benimsemek (to adopt) is transitive, meaning it takes a direct object (bu ilkeyi). When you add the causative suffix to make it benimsetmek (to make someone adopt), the person being made to do the action is shifted into the dative case (herkese).

How is the verb benimsetmek built?