Short answer. It favors whichever party did not cause the confusion, and where two readings are otherwise equally proper, the one most favorable to the party the provision was made for. Rule 130, Section 18 rules against the party in whose sense the other party supposedly understood the term, and prefers the construction favoring the party the provision benefits.
What the law says
When the terms of an agreement have been intended in a different sense by the different parties to it, that sense is to prevail against either party in which he or she supposed the other understood it
Rule 130, Section 18 — Of two constructions, which preferred. Read the full provision →
What the law says
when different constructions of a provision are otherwise equally proper, that is to be taken which is the most favorable to the party in whose favor the provision was made.
Rule 130, Section 18 — Of two constructions, which preferred. Read the full provision →
When the two parties genuinely meant different things
Section 18 addresses a real mutual-misunderstanding situation: the terms of an agreement were intended in a different sense by each party. Rather than simply picking one side's version, the rule resolves it by asking which sense each party supposed the other party understood — that supposed shared understanding is what prevails against each party. This differs from ordinary construction, which typically asks what a term objectively means, by instead asking what each party believed about the other's understanding. This approach makes sense because a genuine mutual misunderstanding, by definition, means neither party's own subjective intent can fairly control; the rule instead looks at what each side believed the other meant, and holds each party to that supposed shared understanding.
The tie-breaker for equally proper readings
Separately, the section addresses cases where different constructions of a provision are otherwise equally proper — no reading is clearly correct over the other. In that scenario, the construction most favorable to the party in whose favor the provision was made is the one adopted. This second rule functions as a tie-breaker of last resort, applied only once other interpretive principles have failed to clearly settle which reading should prevail. It is deliberately positioned as a last resort, only coming into play once ordinary rules of contract construction have already been exhausted without producing a clear answer.
The common thread between both rules
Both parts of Section 18 push toward outcomes that respect what a reasonable party in that position would have understood or intended, rather than letting genuine ambiguity be exploited by whichever side drafted the confusing language, or letting a stalemate simply favor the more aggressive interpretation. Neither rule allows a court to simply pick whichever meaning seems fairer in hindsight; both are anchored to specific, narrow triggering conditions.