Salam,
Brother Wakas has cited 4 arguments in this post (
http://free-minds.org/forum/index.php?topic=9605358.msg327780#msg327780 ) and suggested that any discussion first deal with these before proceeding. So before I present my case I will critique these examples. I will concern myself only with the parts of these arguments which use the Quran to support their points.
1) The first argument by Dr. F.Rahman, defines ribba in his conclusion (1D) as: "
whereby the capital sum is doubled several-fold". But an examination of the words in verse 3:130 shows that it is not the capital, but only the "riba" itself which is being doubled and multiplied. The capital itself does not have to double.
2) J. Islam's argument, I do agree with, but it even though it's premises are all correct, it does not reach a definitive conclusion. Terms are still left vague e.g. "exorbitant interest", but what should qualify as "exorbitant"?
3) M.L Chaudhery's argument is confusing distinct concepts. If we look at the same verses that he himself is citing, the term there is not "charity" but Zakat. And Zakat is fundamentally different than "charity" (discussion of this would require a separate thread). In any case, there is no clear definition of ribba in Chaudhery's argument.
4) Mohf's argument is mistakenly linking the two separate concepts of "Fraud" and "ribba". Fraud requires dishonesty. While ribba can be contractually transparent.
Beyond these arguments, the mainstream usually brings in concepts of "risk", but these are irrelevant to the Quranic description of Ribba which does not mention risk at all.
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Now that the prerequisite has been met, let me present a very clear and unambiguous definition of Ribba derived purely from the description given in the Quran i.e. "increase which is not trade":
Any increase on the returned sum/asset which is in excess of incurred costs (inflation etc.) affecting a reduction in value of the original sum/asset lent. This definition requires no elaborate argument because it is derived from the precise description provided by the Quran.
I would like to state that this thread is not for getting into long discussions on the socioeconomic consequences of such a definition. The issue here is the definition of ribba itself. Unless we can sort out the starting point and agree on this, we can't proceed with building foundational models.