As a general rule, a trust should be explicit as to how decisions should be made among Co-Trustees of a Trust. Fortunately, when a trust document is silent, the California Probate Code provides a number of default provisions to clarify how a trust should operate. 

One such rule is California Probate Code Section 15620, which provides:

Unless otherwise provided in the trust instrument, a power vested in two or more trustees may only be exercised by their unanimous action.

Where there are only 2 co-trustees, this rule makes a great deal of sense, as one would not want only 1 of the 2 co-trustee making a given decision. On the other hand, if a trust has 3 or more co-trustees, it may be preferable to have decisions be made by a majority, on the theory that over 50% of the trustees agree upon a course of action.

The default rules exist to help us avoid questions regarding interpretation of trust documents, but sometimes opting out of certain rules or defining how such decisions should be made can result in a trust being operated in a more efficient manner.