While guilds held a strong control over quality and commerce through the middle ages, they began to decline in importance in the 18th and 19th centuries, given to their perceived disregard for free trade and technological innovation. Amongst their outspoken critics were philosophers Jean-Jacques Rousseau and Adam Smith, who saw them as constraining market forces over prices, wages, and profits. Add revolutionary socialist Karl Marx as another guild critic for their ability to maintain social classes-which conflicted with the classless society which embodies Marxism.

Faced with growing condemnation and the dawn of the British-led industrial revolution, guilds declined in number and in stature. They remain alive today. Historians credit the universities of Bologna, Paris, and Oxford as having originated from guilds of students and masters in the 1200s, with qualitas of education as their contribution to society.

A few years after James Watt perfected his steam engine, Lieutenant General Jean-Baptiste Vaquette de Gribeauval sponsored standardised weapons through a royal order. He is the earliest known advocate for the practice of interchangeability of gun parts, aside from reports of similar advances in China in the time frame of Cicero's orations. The myriad of management details for implementing this revolutionary conversion from craftsmanship to mass production fell to the aforementioned Honoré Blanc. This advance in engineering and manufacturing practice within le système Gribeauval shifted authority for quality from guilds and master craftsman and placed it into every interchangeable part produced and integrated along an assembly line. Business owners were attracted by both the higher volume of assembly line operations and the lower wages paid for tasks not requiring the expertise of a master craftsman. Missing from the financial equations was the impact of shifting the spotlight of quality from the final product of a craftsman and infusing it, instead, into each interchangeable part.

Mass production with interchangeable parts was first demonstrated in 1803 at Portsmouth Block Works in Hampshire; timing coinciding with the height of the Napoleonic War and the strong demand for pulley locks on sailing ships for the British Navy. By 1808, a team led by Marc Brunel had achieved an annual production rate of 130,000 blocks. To appreciate the context of this accomplishment, Richard Beamish, an assistant to Brunel's son, Isambard Kingdom Brunel (who built bridges and tunnels across the U.K.), commented on this feat; "ten men, by the aid of this machinery, can accomplish with uniformity, celerity and ease, what formerly required the uncertain labour of one hundred and ten".

The first American to be exposed to the potential transformative economics of interchangeable parts was Thomas Jefferson, the U.S. Ambassador to France 1785- 1789. After they met, Jefferson invited Blanc to move to the U.S. and share his mass production solution with American companies. He embraced a vision of how this emerging manufacturing system would benefit Americans, as it had the British and French. Rather than leave France, Blanc declined the relocation offer. The American system of manufacturing followed shortly thereafter when Jefferson's dream was shared with Eli Whitney, from Connecticut, leading to the first-ever contract with the U.S. Congress for a product (rifles) assembled with interchangeable parts.

In a radical departure from craftsmanship, in which the master forms all of a product's parts and also aggregates them for assembly operations, the practice of interchangeable parts begins with disaggregation of the component parts of a product. Fabrication follows, often using a series of machine tools (from lathes to milling machines to shapers) to form parts which ideally conform to a series of specification limits(represented by a minimum value and a maximum value, also known as tolerances). Prior to assembly, each part is examined by a quality inspector according to its respective specification limits and graded as either a "good part" or a "bad part". Using the absolute logic of category thinking, all "good parts" are not only good, they are equally good, without variation. Should the specification limits for a hole diameter be a minimum value of 5.000 units (inches, cm, etc) and a maximum of 6.000 units, parts measuring 5.001 and 5.999 would both be rated as "good" and one measuring 6.001 would be rated as "bad," a defect. Good parts are directed to assembly operations and bad parts are scraped, reworked, or, perhaps, measured again.

In a twist on the answer to the second question, notice how the use of tolerances to define the quality categories of good parts and bad parts has changed the predominant answer of 5.999 and 6.001. Had the dimensions been 5.0001, 5.9999, and 6.0001, the distance between the second and third numbers would be even smaller, yet the first two numbers would represent "good parts". In this brief history of quality, herein lies the legend of "the good" parts and "the bad" parts, judged in isolation from each other, rather than judged by how well they integrate, as a craftsman would discern. As an aside, I have heard often-repeated tales of parts slightly outside the specification limits (such as 6.001 is slightly above 6.000) being inspected again, perhaps on second shift, perhaps by a different inspector, awaiting the conclusion that a second, third, if not fourth, result would lead to a value within the specification limits. How likely would it be for a part measuring 5.999 to be inspected again when the specification limits are 5.000 and 6.000?

One hundred years after Whitney's debut with rifles in Connecticut and Brunel's debut with blocks in Portsmouth, the Ford Motor Company Ransom Olds' use of assembly lines for the mass production of interchangeable parts through the use of conveyor belts to create a moving assembly line. In a blitz, moving assembly lines spread the world over, for those companies left behind feared they would perish.

Leave it to actor Charlie Chaplin to satirise moving assembly lines in his 1936 film, Modern Times, for their conceivable adverse impact on factory workers. On close examination, moving assembly lines were built on an 18th century quality foundation of "good parts" and "bad parts" and also guided by Frederick Winslow Taylor's scientific management practices. Credit Taylor with advancing the practice of division of labour, which continues in the 21st century to separate workers, rather than unite them, using a theory of management that closely resembled the theory of interchangeable parts.

Credit Deming with introducing the Japanese economy to a theory of management that challenged the divisionism of Taylorism as well as the divisionism of managing parts and not the interactions between the parts.

Deming's impact on Japan began before his first visits in 1947 and 1950, when Japanese business leaders learned of his role in introducing statistical process control techniques to the U.S. war industry during WWII. His series of summer lectures in 1950 followed an invitation from the Supreme Allied Commander of post-war Japan, General Douglas MacArthur, to share his quality management expertise with statisticians, engineers and senior managers. He was honest in stating his systemic solutions were not "quick fixes" and "it will not happen at once," but also suggested results could be achieved within a few years.

Thirty years later, Larry Sullivan, a senior Ford manager, travelled to Japan to lead an internal effort to study automobile suppliers and the gain explanations for their results. Together, they had captured nearly 30% of the US market share in automobile sales, beginning with zero in 1950 and growing to 3% in 1970. A summary of his findings were published in an article for the American Society for Quality (Variability Reduction: A New Approach to Quality):

In March 1982, I was part of a group that visited Japan and studied quality systems at a variety of automotive suppliers. The most important thing we learned was quality in those companies means something different from what it means in the U.S. - it is in fact a totally different discipline.

As Sullivan and his peers toured Japan and Deming mentored Ford's senior managers and trained thousands of their employees, Motorola introduced six sigma quality as its own quality management strategy. On the reason for selecting six sigma, Motorola offered this explanation:

The concept of zero defects as the achievement of perfection is evidence of the endurance of Blanc's 18th century efforts to transform manufacturing from craftsmanship to a system of interchangeable parts. Six sigma quality has added new life to the zero defects movement launched by Philip Crosby during his employment by International Telephone and Telegraph (ITT), where he retired as the vice president of quality.

Much earlier in his career, he worked as a quality professional in the defence industry. While employed there, he witnessed the known shipment of non-conforming, (defective) hardware to the customer (the U.S. government), albeit at an acceptable level of defects. Crosby set a higher goal for himself, the delivery of zero defects, or 100% "good parts". In doing so, he initiated what was to become known as the zero defects philosophy. In 1979 Crosby released a book on quality management, quality is free. In it, Crosby theorised there are absolutes of quality management, including quality is defined as conformance to requirements, not as goodness nor elegance and the performance standard must be zero defects, not "that's close enough".

While terms like zero defects and defect-free quality are now obvious indications of managing quality through a lens of interchangeable parts, less obvious terms associated with this quality model are yield (the percentage of parts which are "good"), scrap (expenses for the disposal of "bad" parts), rework (expenses for the repair of "bad" parts), non-conformances (parts which are "bad"), process capability indices (various ratios which are based on specification limits), and the cost of quality as well as the price of non-conformance (expenses associated with "bad" parts).