I would like to ask how is obviousness of an invention assessed as it is difficult to appreciate it if you do not have experience of how several inventions have been evaluated. I think we can agree that many inventions (excluding novel chemicals) are using known concepts, i.e. they are based on existing concepts or scientific principles. I.e. it is known that we put catalysts inside the exhaust gas pipe to convert the gases. Putting the catalysts in the turbo would be novel but how obvious is it? In other words, is obvious the 'easy to come up with' or is it something else? Because most of the inventions could be easily generated by experts. Or is it, whether the invention is a common practice among experts already?
It is not a clear science but fortunately an examiner can't just say "seems obvious to me"
In the U.S., first the examiner must find a base reference with an embodiment that has some of the elements of your claim, but not all. It must also be in the same field or could be "analogous art" from a different field where the same problem is being addressed.
Next the examiner must find all of the elements from you claim that are missing in the base reference. They might be from slightly different fields but to convincing should be in the same ball park. In some cases it could another embodiment found in the base reference but usually it is one or more other prior art references.
Now the hard part, the examiner must make an argument as to why someone of ordinary skill in the art would think to combine the teachings of the assembled references to produce the claimed invention. This is clearly susceptible to hindsight bias. Everything seems obvious once you know it.
There used to be a doctrine called TSM that required the examiner to cite either a teaching, a suggestion or a motivation in the prior art to combine the teachings. A SCOTUS case, KSR has had much commentary. It said TSM was a good tool but not the only way to establish obviousness. Added was "obvious to try", "only a few things possible to try" and the issues of "likeliness to succeed" and "unexpected results" were introduced.
This has made it harder for an applicant to overcome an obviousness rejection. One argument that still works well is that, if to turn a reference into the claimed invention it has to be made unfit for its original purpose. Making a bucket unable to hold anything would be an example.
In Europe the problem-and-solution approach is used most of the times because it is said to be an objective assessment of inventive step/non-obviousness. Below I reproduce some points about it. The same methodology is used in some other countries, most notably China and Japan.
In the problem-solution approach, there are three main stages: (i) determining the "closest prior art", (ii) establishing the "objective technical problem" to be solved, and (iii) considering whether or not the claimed invention, starting from the closest prior art and the objective technical problem, would have been obvious to the skilled person.
(i) "closest prior art": single reference that discloses the combination of features which constitutes the most promising starting point for a development leading to the invention. In selecting the closest prior art, the first consideration is that it must be directed to a similar purpose or effect as the invention or at least belong to the same or a closely related technical field as the claimed invention. In practice, the closest prior art is generally that which corresponds to a similar use and requires the minimum of structural and functional modifications to arrive at the claimed invention
(ii) "objective technical problem": one establishes in an objective way the technical problem to be solved. To do this one studies the application (or the patent), the closest prior art and the difference (also called "the distinguishing feature(s)" of the claimed invention) in terms of features (either structural or functional) between the claimed invention and the closest prior art, identifies the technical effect resulting from the distinguishing features, and then formulates the technical problem
(iii) "would have been obvious to the skilled person?": the question to be answered is whether there is any teaching in the prior art as a whole that would (not simply could, but would) have prompted the skilled person, faced with the objective technical problem, to modify or adapt the closest prior art while taking account of that teaching, thereby arriving at something falling within the terms of the claims, and thus achieving what the invention achieves