Legal Question in Administrative Law in California

Civil Code section 2309 says "An oral authorization is sufficient for any purpose, except that an authority to enter into a contract required by law to be in writing can only be given by an instrument in writing."

This is the so-called "equal dignities rule."

Thus, an agent may be authorized orally to buy groceries, but not real estate.

No, but just try to prove the terms and details without one, once a dispute arises.

Just to clarify Mr. Whipple's answer, in general only a contract for the transfer of real estate need be written as opposed to oral [how could you record a transfer of property unless it were in writing?]. Mr. Nelson is correct that proving what was agreed to is much easier if it is in writing.