A contract cannot be formed without consideration.
Consideration may be either:
1) a benefit conferred or agreed to be conferred upon the person making the offer [counteroffer] [or some other person], to which the person is not otherwise entitled; or
2) a detriment suffered or agreed to be suffered by the person [or some other person] to whom the offer [counteroffer] is made.
A written contract is presumptive evidence of consideration. [The burden of showing a lack of consideration sufficient to support a written contract lies with the party seeking to invalidate or avoid it.]