Four corners of an instrument describes the principle that a document (such as a contract, deed or will) should primarily be interpreted by reference to the wording contained within its own text, rather than external material. The “four corners” are the physical and metaphorical boundaries of the document.In UK and Irish practice, the phrase is most commonly used in contractual interpretation and construction of deeds and other formal instruments. Courts in England and Wales, Scotland, Northern Ireland and Ireland generally adopt a similar approach: the starting point is the natural and ordinary meaning of the words used in the document, read as a whole, in context.The expression is not a statutory term but a descriptive doctrine developed in case law and commentary, sometimes contrasted with broader contextual or purposive interpretation. Modern authorities accept the relevance of surrounding circumstances and commercial common sense, but the four corners principle underlines that extrinsic evidence cannot be used to re‑write clear wording.Practically, this principle guides drafting (ensuring the instrument is complete and self‑contained) and litigation strategy (focussing on the language actually agreed or executed).