5.3 Could-would approach 

In the third stage 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 (see G‑VII, 4).

In other words, the point is not whether the skilled person could have arrived at the invention by adapting or modifying the closest prior art but whether the skilled person would have done so because the prior art provided motivation to do so in the expectation of some improvement or advantage (see T 2/83). Even an implicit prompting or implicitly recognisable incentive is sufficient to show that the skilled person would have combined the elements from the prior art (see T 257/98 and T 35/04). This must have been the case for the skilled person before the filing or priority date valid for the claim under examination.

When an invention requires various steps to arrive at the complete solution of the technical problem, it is nevertheless regarded as obvious if the technical problem to be solved leads the skilled person to the solution in a step-by-step manner and each individual step is obvious in the light of what has already been accomplished and of the residual task still to be solved (see T 623/97 and T 558/00).