When someone has “possession” of something, he takes control of it. Possessions are items owned by people. Sometimes they own these things legally and taking it from the person constitutes theft. Other times, the person has control over the possession. Even when someone temporarily occupies something, such as a car, he is sometimes considered to have possession of that object. “Concession” only refers to the initial stages of ownership, when someone gives something, and not the long-term ownership of something. Also, concessions are not temporary.
“Possession” sometimes refers to something taking over a person, such as a passion, spirit or idea. When someone enters a state of mind where he takes on a different persona, he is sometimes called “possessed.” Concessions never take over anyone. “Possession” can refer to the object possessed. For example, the objects in a baseball player’s locker can be his possessions. “Concession” never refers to a tangible object, but always a process.
Possessive refers to the use of an apostrophe and sometimes an “S” at the end of a word to denote the subject owns an object mentioned later in the sentence, such as “Rupert’s media empire." Concession is not a grammar term.
A concession involves someone accepting that something is correct or granting someone something. When Pat makes an argument that changes Pam’s mind, Pam is conceding the argument. Possessions are not related to arguments.
Concession is the process of granting something to someone. Concession can refer to a grant of property in return for a service. “Concession” is a process of giving something, while possessing something is the process of taking.
Some people concede not because they agree, but only to reach an agreement with another person, usually reluctantly. However, someone does not usually possess something to reach an agreement, unless she is taking it hostage.