Learned pronouns: εαυτού, αλλήλων, ουδείς
The frozen reflexive, the reciprocal with no nominative, and the absolute negator of formal Greek.

Αλλήλων: reciprocity
Αλλήλων has no nominative — logically so: “one another” cannot be a subject. You meet it in the genitive and accusative, and above all in compounds: αλληλεγγύη, αλληλοβοήθεια, αλληλεπίδραση.
- Οι δύο πλευρές κατηγόρησαν η μία την άλλη.The two sides accused one another.
- Η αλληλεγγύη μεταξύ των κρατών-μελών.Solidarity among the member states.
Ουδείς and the frozen reflexive
Ουδείς / ουδεμία / ουδέν replaces κανένας in the formal register: «ουδεμία ευθύνη», «ουδέν σχόλιο». The ancient reflexive survives mainly in καθ’ εαυτόν, δι’ εαυτού, αφ’ εαυτού — unanalysable, learned as they are.
The same topic at other levels
Pyetjet e bëra shpesh
What does «αλλήλων» mean, and why does it have no nominative?
«Αλλήλων» expresses reciprocity — “one another”. It has no nominative because “one another” can never be the subject: it appears in the genitive, the accusative and above all in compounds such as «αλληλεγγύη» (solidarity).
When do Greeks say «ουδείς» instead of «κανένας»?
«Ουδείς / ουδεμία / ουδέν» is the formal-register “no one, none”: «ουδεμία ευθύνη» (no responsibility whatsoever), «ουδέν σχόλιο» (no comment). In everyday speech, say «κανένας».
What does «καθ’ εαυτόν» mean?
It is a frozen ancient reflexive meaning “in itself, by itself”: «το πρόβλημα καθ’ εαυτό» (the problem in itself). Such blocks — «δι’ εαυτού», «αφ’ εαυτού» — are learned as they are; they can no longer be parsed in Modern Greek.