(a) Where all the parties who unite in a promise receive some benefit from the consideration, whether past or present, their promise is presumed to be joint and several.

(b) A promise made in the singular number, but executed by several persons, is presumed to be joint and several.
SOURCE: CC § ‘1659, 1660 (on the same subject) joined. ‘1659 is subsection (a)
and ‘1660 is subsection (b).