To have a valid contract, subject matter must be determinate or specific (law on loss, deterioration, fruits, applies only to determine subject matter) and sale is unconditional (perfection)
Delivery of subject matter is the mode which transfers ownership to the buyer
Not a title but a mode; tradition transfers ownership (needs delivery)
Risk of loss passes at perfection (even if ownership has not yet been transferred)
COMMON LAW
Perfection of unconditional contract of sale covers goods that are determinable
Perfection with availability of subject matter for delivery is the mode which transfers ownership to buyer;
Tradition is merely a means to perform obligation
Res perit domino; owner bears risk of loss