In OEthe Infinitive resembled the Noun and had the category of Case (only two Cases – Nominative (Nom) and Dative (Dat)):
e.g. OE Nom writan (uninflected) – Dat to wrītanne (inflected, indicated direction or purpose).
In ME the Infinitive lost the Dative Case (the inflected form) and only one form was left:
e.g. ME (to) writen.
Particleto remained in NEas a formal sign of the infinitive with no meaning of direction or purpose:
e.g. NE (to) write.
Though sometimes the traces of these meanings are still visible:
e.g. He came to feed the horses (purpose).