Bava Batra 29: Why Three Years for Chazaka?; Proof of Possession

Why have the rabbis understood that chazaka, presumptive ownership, is established after three years?  The Gemara uses a number of examples to illustrate the rabbis' reasoning.  It explains that after one year, an owner might let it go when another person profits from use of his land.  After two years he might do the same.  But after three years had passed, an owner would stand up and claim his land.  

Another example includes a document that validates purchase of land.  A person would hold onto that document for the first year, and the second year, but after that it was reasonable to assume that the land belonged to him due to his use of the land for years.  

The Gemara also speaks to using the testimony of neighbours to validate a person's possession of land or property over time.  Examples of shared ownership create particular difficulties.  For example, two neighbours shared ownership of a maidservant where they would have her serve each of them on alternate years.  When a third person claimed his inclusion of this shared ownership, Rava ordered that there is no chazaka present for any of the three of them.  However, if documents detailing their ownership are found, then there is not a need to argue chazaka.

How can one establish chazaka over partially used land?  If a person does not use a part of the disputed land, he can only claim rights to the parts of the land he has used.  If the entire area is rocky, then he must send animals out onto the land or spread produce there to establish his ownership.  

Our Gemara raises one last question: what if a person states that they have not been in town to contest another person's chazaka?  Who should be asked to prove a claim to the property, the possessor?  Or the claimant (the person who says that this property was his and that no permission was given for residence in his absence)?  We will learn more about this in tomorrow's daf.