Proposal, proposition denote something which is proposed to another for consideration.
Proposal usually carries a clear suggestion of the act of proposing; thus, one receives a proposal, or entertains a proposal, or listens to a proposal. It also commonly implies an offer (as of oneself as a husband, or of a sum of money in return for the transferring of a piece of property).
But it may imply the suggestion of a scheme, a plan, or a project which may be accepted or rejected at the will of the one to whom it is proposed.
Proposition applies primarily to a usually affirmative statement that is propounded for discussion, argument, proof, or disproof.
The term is also applicable to an implied or expressed principle that is or may be questioned or is regarded from the point of view of its truth or its falsity.
Proposition has been and to a restricted extent still is used instead of proposal in the sense of a proposal made formally that some course of action be followed, some policy be adopted, or some honor granted.
Proposition may replace proposal in implying an act of proposing, but in such use it and especially the corresponding verb proposition may carry a hint of irregularity or impropriety that proposal lacks; thus, one offers a proposal of marriage but a proposition of less formal sexual relation.