Difference Between Ownership and Possession
http://www.differencebetween.com/difference-between-ownership-and-vs-possession/

Przykłady użycia według słownika: Wielki słownink PWN-Oxford

possession

1. (state of having) posiadanie n (of sth czegoś);
according to the information in my possession- według posiadanych przeze mnie informacji;
to be in possession of sth- mieć coś; być w posiadaniu czegoś fml;
to be in sb’s possession- być w posiadaniu kogoś fml;

she wasn’t in full possession of her faculties- nie była w pełni władz umysłowych;
to come into his/her possession- dostać się w jego/jej posiadanie fml;
how did you come into possession of this document?- jak wszedłeś w posiadanie tego dokumentu? fml;

to get possession of sth- wejść w posiadanie czegoś fml;
to have possession of sth- posiadać coś fml;
to take possession of sth Jur- objąć coś w posiadanie [house, property];
Mil zająć coś- [town, region]

2. Jur (illegal) (nielegalne) posiadanie n (of sth czegoś);
to be charged with illegal possession of arms- zostać oskarżonym o nielegalne posiadanie broni;
he was found in possession of drugs- znaleziono przy nim narkotyki

3. (sth owned) własność f; (colonial) posiadłość f;
this is my most treasured possession- to jest najcenniejsze, co posiadam;
health is the most important possession- zdrowie jest najważniejsze


ownership

(proprietorship)własność f; (state of being an owner)
posiadanie n; (right of possession)- prawo n własności;
joint ownership-współwłasność;

private/public ownership- własność prywatna/publiczna;
car/home ownership- posiadanie samochodu/domu;
share ownership- udział w kapitale akcyjnym;

to acquire ownership of sth- wejść w posiadanie czegoś;
the growth of home ownership- wzrost liczby właścicieli domów i mieszkań;
to be in or under private ownership- być własnością prywatną;

to take sth into public ownership- znacjonalizować coś;
to be under new ownership- mieć nowego właściciela;
under her ownership the club has flourished- klub kwitnie od czasu, gdy została jego właścicielką;
to provide proof of ownership- przedstawić dowód własności

Dodatkowo:
Possession versus Ownership [1]

Although the two terms are often confused, possession is not the same as ownership. No legal rule states that "possession is nine-tenths of the law," but this phrase is often used to suggest that someone who possesses an object is most likely its owner. Likewise, people often speak of the things they own, such as clothes and dishes, as their possessions. However, the owner of an object may not always possess the object. For example, an owner of a car could lend it to someone else to drive. That driver would then possess the car. However, the owner does not give up ownership simply by lending the car to someone else.

The myriad distinctions between possession and ownership, and the many nuances of possession, are complicated even for attorneys and judges. To avoid confusion over exactly what is meant by possession, the word is frequently modified by adding a term describing the type of possession. For example, possession may be actual, adverse, conscious, constructive, exclusive, illegal, joint, legal, physical, sole, superficial, or any one of several other types. Many times these modifiers are combined, as in "joint constructive possession." All these different kinds of possession, however, originate from what the law calls "actual possession."

1.http://legal-dictionary.thefreedictionary.com/possession

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