ABSTRACT
Categorical principles guide our thinking and help us classify ideas and observations. There are many categorical principles, and consequently many different classifications are possible. It is important to understand this distinction because in our own cases involving continuous phenomena such as color gradations or the severity of flaws, classification is extremely difficult unless standards for deciding are shown by means of numerical values and limit samples. An object may be either concrete or abstract. A concrete object can be apprehended by means of one or more of the five senses: sight, touch, hearing, smell, and taste. Even when products are actually being made, however, the technical worker's function of standing by the machine is also abstract. Checklists would be unnecessary if people never forgot things. Production workers who forget to attach parts or mistakenly attach the wrong parts are scolded by their supervisors and urged to pay more attention.
