Patent ambiguity in written instruments bars extrinsic evidence to determine alternative terms or complete omitted particulars.

Section 93 excludes evidence of facts intended to explain the meaning of a written instrument where its language is, on its face, ambiguous or defective. The prohibition prevents oral or other extrinsic evidence from identifying an intended meaning or curing an apparent defect. It applies where an agreement states alternative prices without indicating the applicable price and where a deed contains unfilled blanks.

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