Renowned classical lexicons describe that this Root leads to the perception of purity, sincerity and worthiness of a thing; it signifies heart; and secondly turning-revering-inverting-changing of a thing, its mode or manner of being. It denotes turning over and over, or upside down, or to revolve repeatedly a thing to investigate, scrutinize or examine to know or determine its inner self; and what might be the issues and affairs. The turning over and over is exemplified like the sweltering of a serpent on hot sand of desert.
Lane Lexicon: inf. n. قَلْبٌ, He altered, or changed, its, or his, mode, or manner, of being; He inverted it; turned it upside-down; turned it so as to make its upper most part its undermost; heart
Semantic domain: Human body
Sub field: Heart
Grand Qur’ān has nowhere suggested or even hinted that: and : the hearts are synonym, synonymous or interchangeable. It is derived from Root "ف ء د". The basic perception and signification described by lexicons is that of heat of ashes and is used to portray baking of dough: a soft elastic mixture of flour and water, often with other ingredients such as oil, butter, salt, and sugar, that becomes bread or pastry when baked. Raw material is like data and the yield of the process, the baked product, is like the information obtained by integration of data input.
Therefore, refers primarily to that faculty and establishments in human body that corresponds to the basic perception infolded in its Root. Each word of text is unique. Every word is essentially different from another notwithstanding its proximity in some aspects. The choice of words in the text of Qur’ān must not be altered or substituted by another Arabic word for convenience of translation in the target language. It must be avoided particularly when intention is to co-relate it with generally held perceptions and beliefs of majority of people at any given point in time. We do not have the absolute knowledge of Universe nor of our own bodies. We will remain in the process of learning till the blow of Last Sound in the trumpet, the real big bang. Moreover, no one adopts such sort of attitude and behaviour with any other book of the world, therefore, why this attitude is met to Qur’ān which too is the Book.