Ijma and qiyas are two things that can/could only be used after the death of Muhammad. It's in hadith so not an invention or innovation.
Qiyas in a nutshell is the deriving of a ruling on a new issue using older rulings.
So khamr (intoxication) caused by alcohol can be used to derive a ruling on modern day drugs that didn't exist in that time.
Or drawing of blood these days during fasting is allowed because of cupping in the Prophets days.
I think we're talking at cross-purposes here. I'm talking about logic as a philosophical concept and how differing approaches to logic (inductive and deductive reasoning, syllogism etc.) and the inherent subjectivity of logic, led to qiyas operating differently amongst different groups at different times, producing different rulings. This is why some Muslims at the time disavowed qiyas altogether. The logical methods employed were seen as inherently subjective and thus would inevitably lead to divergence of belief, which was seen by some to contradict the Qu'ran.
To take your example of khamr as referenced in the Qu'ran (disregarding the relevant hadith for the moment as it wasn't universally accepted in the period I'm talking about). The interpretation of the words of the Qu'ran on khamr to mean a ban on all alcohol requires one to make a logical argument along the lines of:
"The Qu'ran says we shouldn't drink wine. The Qu'ran says we should not pray under the influence of drink. Therefore the reason we cannot drink wine is because it leads to drunkeness which is not allowed during prayer. Therefore any substance which leads to drunkeness is also haram."
Point being, that argument relies on both a particular approach to logic which we find quite, well, logical, but which wasn't universal at the time, and on a particular application of that logic which wasn't universally agreed upon. For example, you will find arguments up until at least the 12th century that, variously:
a) the Qu'ran should be taken as read without applying logic to extrapolate as this applies subjective human interpretation to divine words. Therefore, khamr refers specifically to wine, meaning wine is haram, whereas other alcohol is not.
b) khamr should be inferred to refer to the state of intoxification generally, meaning that consumption of amounts of alcohol which don't lead to drunkenness is allowed
c) a combination of the above, khamr refers both to wine and to the state of drunkenness. Wine is therefore haram, other drinks were permissable up to an agreed point of intoxification
These are all valid interpretations of the Qu'ran's references to khamr. In addition, the idea of khamr meaning a particular threshold of intoxication led to some schools of Islamic jurisprudence having to develop applicable and demonstrable definitions of intoxification, which obviously differed between different areas. This bar was often set incredibly low, for example being somewhat intelligible, being able to distinguish between a man and woman, etc.
To be clear, I'm not trying to undermine Islam here, or any of the Abrahamic religions, or imply that they stole anything from Classical Greece. I'm just talking about the impact of philosophy (in this case, approaches to logic) on religious law throughout a specific time period. I imagine those debates are less important in faith nowadays, both as logic is no longer a massively contested concept in everyday life, and as philosophy has fragmented over the last millenium and people tend to focus on one discipline. Philosophers used to be all-rounders in a way we don't really see now and there wasn't a clear delineation drawn between theology, philosophy and what we'd now call "hard science". Ibn Sina is a good example, as amongst other things, he developed concepts of metaphysics and logic in response to Aristotle and earlier Muslim philosophy, and then used them to write an ontological argument for the existence of God which was incredibly influential (across all the Abrahamic faiths) for centuries after his death, as part of a text which was also incredibly influential over medicine and psychology for centuries after his death.
