A variation (sometimes referred to as a change) is an alteration to the scope of work originally specified in the contract, whether by way of an addition, omission, or substitution to the works, or through a change to the manner in which the works are to be carried out. The particular nature of the construction process makes the subject of variations important. Inevitably, because the parties cannot anticipate everything which may happen or where a contract is agreed before the design or scope of works are fully finalised, frequent changes are often required. Unless a variation is instructed, a contractor is required to follow the works as originally specified—otherwise it would be in breach of contract. When the employer asks the contractor to vary the work, the variation is being made under the contract rather than to the contract itself. For guidance on changes to the terms of the contract itself, see Practice Note: Contract variation. While touched on briefly below in various parts, for a more detailed analysis of the specific variation