If a contract has been substantially performed by one party to a contract, but there are minor deviations, the other party is not absolved from its obligations. Damages in keeping with the deviation (or defect) may be deducted.
The concept of substantial performance applies most often to construction contracts when, for example, a contractor installs a component outside of the agreed-upon specifications. For example, if a bathroom renovation calls for porcelain doorknobs and brass ones are substituted in error, the homeowner still would be charged with paying almost the entire stipulated price.