What is understood by the coming together and separation of parts is that they may separate while retaining their essential nature. Water, for example, may disperse until its parts become extremely small, yet it remains water. The same applies to mercury and similar substances. But once it is subsequently transformed into air, it is no longer water or mercury. Whoever claims that its parts remain after this transformation just as they remain when reduced in size contradicts both sense perception and reason. No part of water or a similar substance can be conceived of except as water. Once it becomes air, however, no part of that air is water; rather, every part of the air is air.

Likewise, pieces of firewood may be broken into increasingly smaller pieces. But once it becomes ash, the parts of the ash differ from those of the firewood: these are not the same parts. Thus, a thing’s remaining while its properties change is one thing, and the transformation of its essential nature is another.

Language and religious law therefore distinguish between the two, treating each as a different category in all rulings. This is unlike the case in which a thing retains its essential nature while its properties change. Thus, a ruling concerning gold and silver that applies to the substance itself—as with ribā (usury), for example—continues to apply even if its form and shape change, whether it is gathered into a single mass