In this paper we analyse the way in which contract proposals can be expressed in order to be considered as well formed. We limit ourselves to a micro-world containing two parties in interaction (a Speaker and a Hearer), and two utility values (positive and negative) attached to the exchanged goods. A contract is defined as well formed if the exchange would result in an increase in utility for both parties. In that micro-world, 64 forms of contract proposals are formally definable. However, only 32 forms are permissible to express a well-formed contract. These forms convey the same meaning but differ in their conditions of use. Two of them are identified as more basic (canonical) forms to which all the others can be reduced from a semantic point of view. A partition of the 32 well-formed proposals into two subsets of equal size can be made on the basis of these two canonical forms. One subset is made of forms that can degenerate into non-contractual forms (threats) provided a condition on one of the utilities is satisfied, whereas the forms of the other subset cannot degenerate.