Excerpt from Cal. Commercial Code 9203 governing security interests in personal property

[Editorial note:  A common example of a security interest is a right taken by a bank to repossess your car if you default in repaying the loan from the bank that enabled your purchase of the car.  This is analagous to a mortgage on real property.]

. . .

(b) [Enforceability.] Except as otherwise provided in subsections (c) through (i), a security interest is enforceable against the debtor and third parties with respect to the collateral only if :

(1) value has been given;

(2) the debtor has rights in the collateral or the power to transfer rights in the collateral to a secured party; and

(3) one of the following conditions is met:

(A) the debtor has authenticated a security agreement that provides a description of the collateral and, if the security interest covers timber to be cut, a description of the land concerned; . . .

[Other conditions for special types of collateral are not reprinted here.]