Which of the following is NOT one of the four methods of specifying?

The method of specifying that is NOT included among the recognized four methods is the virtual specification. The four commonly accepted methods of specifying in interior design are performance, proprietary, reference standard, and prescriptive specifications.

Performance specifications define the required outcomes or results expected from a particular product or system, focusing on the functionality and performance metrics rather than the specific components. Proprietary specifications detail specific products or brands that must be utilized, ensuring a particular quality or aesthetic is achieved. Reference standard specifications refer to established benchmarks or standards issued by recognized authorities to ensure compliance with safety and quality measures.

In contrast, virtual specifications do not hold a recognized place in traditional methods of specifying because they imply a broader and often less tangible concept related to digital representations or conditions rather than concrete products or performance metrics. This difference highlights why virtual is the correct answer to the question about which method of specifying does not belong to the standard recognized categories.