5.3 Could-would approach 

At 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, when faced with the objective technical problem, to modify or adapt the closest prior art in the light of that teaching in such a way as to arrive at something falling within the terms of the claims and thus achieve 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). It must be shown that the skilled person would have done so before the filing or priority date valid for the claim under examination.

Even if various steps need to be taken to solve the technical problem entirely, the invention will still be regarded as obvious if the technical problem leads the skilled person step by step to its solution and each individual step is obvious in the light of what has already been accomplished and what still remains to be solved (see T 623/97 and T 558/00).