There is not a single universal concept of Ownership. Consider the following definitions:
Wikipedia
Ownership is the state or fact of exclusive rights and control over
property, which may be an object, land/real estate or intellectual
property. Ownership involves multiple rights, collectively referred to
as title, which may be separated and held by different parties.
Business Dictionary
The ultimate and exclusive right conferred by a lawful claim or title,
and subject to certain restrictions to enjoy, occupy, possess, rent,
sell, use, give away, or even destroy an item of property.
Ownership may be corporeal (title to a tangible object such as a
house) or incorporeal (title to an intangible object, such as a
copyright, or a right to recover debt). Possession (as in tenancy)
does not necessarily mean ownership because it does not automatically
transfer title.
Karl Marx in The German Ideology
The various stages of development in the division of labour are just so
many different forms of ownership, i.e. the existing stage in the
division of labour determines also the relations of individuals to one
another with reference to the material, instrument, and product of
labour.
These definitions are not equivalent. Business Dictionary only considers ownership when conferred by law. While Wikipedia only considers facts about control and exclusive rights. Marx's definition is pretty much in agreement with Wikipedia's and correctly identifies the source of ownership : relationships among individuals. The laws mentioned by Business Dictionary are one kind of such relationships that give rise to ownership, but not the only ones.
This source of ownership, relationships among individuals, is quite universal. The way individuals relate to each other may give rise to different forms of ownership, but this will always be the source of ownership.
A practical example of conflicting definition of ownership over material things would be :
- An Android phone with full access. You completely control which software you can install on it at all levels.
- An iPhone phone. You do not control which software you can install on it. A second party, Apple, gets to restrict which software you can install on it.
Some people would argue you can only truly own the Android phone while the IPhone phone would be at best partially owned. Others would claim you equally own both.
Another example of conflict in definition of ownership would be intellectual property.
Thomas Jefferson in Thomas Jefferson to Isaac McPherson:
If nature has made any one thing less susceptible than all others of
exclusive property, it is the action of the thinking power called an
idea, which an individual may exclusively possess as long as he keeps
it to himself; but the moment it is divulged, it forces itself into
the possession of every one, and the receiver cannot dispossess
himself of it. Its peculiar character, too, is that no one possesses
the less, because every other possesses the whole of it. He who
receives an idea from me, receives instruction himself without
lessening mine; as he who lights his taper at mine, receives light
without darkening me.
Here Jefferson was talking about patents. But the concept may be applied to any idea. If a song is copied the copyist has a new song (receives new light) but the "owner" of the original work has the same amount of songs (without darkening me). Compare this with taking an apple from a shop; the shop owner has one less apple and the taker one more. This means that the concept of ownership when applied to ideas is quite different than when applied to materials things.
Yet others would argue that songs can be owned:
The Recording Industry Association of America (RIIA) About piracy:
We also work hard to protect artists and the music community from
music theft.
Here RIAA is arguing that songs can be subjected to theft which implies that songs can be owned.
And indeed RIAA is right. Songs can be owned. Since, as seen before, ownership stems from relationships among individuals. And some of those relationships, called laws, grant forms of ownership over those songs.
Of course there are other kinds of relationships among individuals like The Pirate Bay. This means that ownership of songs, and other ideas, is quite limited these days.
How would someone define something as their own?
It is your own if the relationship you have with the individuals around you grant you exclusive rights and control over that something.
How would that person know if whatever he/she is trying to possess has
been possessed by anyone?
You ask those in the vicinity.
