Objects of personal property can be lost, mislaid, or abandoned. A lost item is something that the owner involuntarily parted with and is in an unknown location, a mislaid item is something that was intentionally placed in a location, but the location is then forgotten, and an abandoned item is personal property that the owner intentionally parts with and relinquishes the right to own. The distinction is important too, because the owner of a lost item still has technical legal ownership of the lost or mislaid thing, and that ownership is typically superior to the ownership of the finder. By contrast, the finder of abandoned items has legal ownership of the abandoned thing. Oregon law allows a person to transfer an item from lost/mislaid status into abandoned property status through publication of a notice of the unclaimed property.
Similarly, a person can agree to abandon items, thereby relinquishing their ownership. Many contracts will state something to the effect of “items left behind at closing are considered abandoned,” therefore creating an affirmative documented proof that the person’s claim to the items is severed.
Remember though, a person can only relinquish their own personal claim to property. When you purchase a property with an attic full of antiques hidden behind a false wall, you only have ownership of those items if (1) the contract said the Seller abandoned their interest in things left behind after closing, and (2) the items belonged to the Seller at the time of the sale. If the Seller didn’t know about the antiques or never gained possession of the lost or mislaid items when the seller first came into possession of the property, the original owner [or their descendants] may still be able to lay claim to the items.
Oregon REALTORS® Forms address property left by seller in Section 46 of Form 1.1, the Residential Real Estate Purchase and Sale Agreement. Also, keep in mind that landlords must follow special statutory rules for property abandoned by tenants. See ORS 90.425.