A Difference Between Friends and Acquaintances

I have had reason within my own personal life to ponder the difference between being friends with someone and being merely acquainted with them. One major difference can be summarized as follows:

• Friend: Someone you want to spend time with and are willing to actively work to make time for as it is possible to do so.
• Acquaintance: Someone who you spend time with incidentally, not intentionally or with whom you are not willing to make time for beyond the incidental. People you only see in class or at work would could as such.
  

The sticky bits are with respect to

1. a person you simply do not have time for regardless of whether or not you would work to make time if you had any. I would say this is more a friend than an acquaintance.
2. People you have been acquainted with over an extended period. Then this could be said to have grown into friendship.
3. People you were friends with but now no longer spend time with.

So as even I must admit, the above distinction leaves something to be desired. But I never said it was the whole definition.