Many authors have tried to create definitions of design in line with their design practices. Design theory based on such practice-based definitions and the definitions themselves are problematic. How do I know? I've tested hundreds of definitions of design. There is one definition of design that stands out by addressing the practical and epistemological problems of other definitions. Even better, it is really simple and straightforward:

A design is a specification for making or doing something

Or in plain English,

A design is a set of instructions how to make or do something

This then extends into:

Designing is the activity of creating designs

and

A designer is someone or something that creates designs

In line with the above

Design Theory is theory describing the creating of designs

and similarly

Design research is research aimed at producing design theory

The essence is clear 'A design IS a specification, description or set of instructions to make or do something'. This is a 'necessary and sufficient' definition, i.e. a design is not anything else.

What that specification (the design) specifies (the something to be actualised by using the information provided by the design) and the quality or qualities of it are entirely secondary, subsequent and irrelevant to the definition of design itself.

A benefit of this approach is it distinguishes between and separates a design and the things constructed or done using the instructions in that design.

That is, it defines a difference between a design and a product.

In addition, this approach also distinguishes and separates the creation of designs from the activities of art and craft where these do not result in the creation of a design whose instructions are used to produce the artefacts or other outputs.

Even better, this definition of design and its ancillaries, also address the human vs machine  definition problem in design as well as many other  areas of design theory conflict involving creativity, emotional and rational cognition, and relationships between the creation of a design and the multitudes of ways that might be undertaken.

For most involved in design research, the use of the above definitions will simplify and clarify their research problems,  theoretical analyses, data collection, literature review and their critique and synthesis of theory.

© T. Love 2008, 2015