EXAMPLE 1
A PhD student constructs a new plasmid according to the scheme devised by their supervisor. They do not become an inventor because they were merely following the directions. Their supervisor is the true inventor.
Participation in the reduction of the invention, without more, does not make an individual an inventor.
Someone participating in the reduction to practice AND contributing to the final, complete conception is an inventor, but participation only in the "reduction to practice" does not warrant inventorship.
EXAMPLE 2
A manufacturer makes a new product according to provided specifications is not an inventor because they merely contributed to the reduction to practice.
As sometimes occurs, the original conception provides a prototype or basis for the invention but does not represent the final invention which is eventually claimed. An inventor can seek the help of others when perfecting the invention without the helper necessarily becoming an inventor.
Furthermore, an individual who only makes changes to the production method while reducing the invention to practice is not an inventor.
EXAMPLE 3
A post-doctoral physicist adds a feature to a prototype their laboratory is working on. The additional feature will give the prototype another useful purpose. If the new purpose is claimed in the patent application, the post-doc has contributed to the conception of the invention and, as a result, is an inventor.