Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[4] And perhaps we should also add the qualification that the feeling of goodwill must be known to its object. For a man often feels goodwill towards persons whom he has never seen, but whom he believes to be good or useful, and one of these persons may also entertain the same feeling towards him. Here then we have a case of two people mutually well-disposed, whom nevertheless we cannot speak of as friends, because they are not aware of each other's regard. To be friends therefore, men must （1） feel goodwill for each other, that is, wish each other's good, and （2） be aware of each other's goodwill, and （3） the cause of their goodwill must be one of the lovable qualities mentioned above.