According to Aristotle, who thought about and wrote extensively about friendship, there are three main reasons why one person might become a friend to someone else: one might become a friend to someone because he or she is virtuous; or because he or she is useful; or because he or she provides pleasure. Another way of describing these three reasons are: friendships formed for mutual caring; friendships formed for utilitarian reasons; and friendships formed for sharing pleasure.

Here are paraphrased descriptions of Aristotle's categories of friendship:

1. When an individual recognizes that the other person is someone of good character, and they spend time with each other, engaged in activities that exercise their virtues, then they form one kind of friendship. A genuine friend is someone who loves or likes another person for the sake of that other person. Wanting what is good for the sake of another is called "good will" (eunoia), and the friendship is based on reciprocal good will, provided that each recognizes the presence of this attitude in the other.

2. People form friendships because each individual regards the other as the source of some advantage to herself or himself. This is the category of friendship where one spends time with another person because he or she benefits from the friendship, not because of the kind of person he or she is, but only because of the advantages to oneself - so one is not a friend towards the other person, but only towards the profit that comes one's way.

3. People form friendships for pleasure - they enjoy another person's company and participate in pleasurable activities. This type of relationship is purely based on people getting together to do things they like, such as going to sporting events, seeing movies, dining out, going to the beach, going to concerts, etc.

Artistotle felt that relationships based on profit or pleasure should not be called friendships at all because friendships should be based on feeling good will toward each other and wishing good things for each other. Friendships based on virtue are friendships in which each person benefits the other - these are friendships most of all, and since each enjoys the trust and companionship of the other, there is considerable pleasure in these relationships as well. To have a friend is to want to benefit someone for the other person's sake - it is not a self-interested strategy - for when we know how to benefit a friend for his or her sake, we are happy.

It is generally believed, and consistent with Aristotle's description of true friendship, that value found in friendships is often the result of a person demonstrating the following characteristics on a consistent basis:

1. the tendency to desire what is best for the other

2. sympathy and empathy

3. honesty, including situations where it may be difficult to speak the truth, especially in terms of pointing out the perceived faults of one's counterpart

4. mutual understanding and compassion

5. trust in one another (the ability to express feelings - including in relation to the other's actions - without the fear of being judged or abandoned)

6. the ability to go to each other for emotional support and

7. positive reciprocity - a relationship based on equal give and take between the two parties.

Aristotle's categories along with these seven characteristics help to clarify what true friendship is as well as how to be a true friend.