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A sale is therefore valid only if it is free from substantial uncertainty, since the minor uncertainty inseparable from sales is regarded as negligible and tolerated.
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Scholars disagree over the invalidity of particular contracts only because they differ over the uncertainty involved: is it substantial uncertainty, covered by the Prophet’s prohibition, peace and blessings be upon him, of sales involving uncertainty, which renders the contract invalid? Or is it minor uncertainty, regarded as negligible and tolerated in sales, which does not invalidate the contract?
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Substantial uncertainty that invalidates a contract concerns three things: (first) the contract itself; (second) either of the two countervalues—the price or the item sold—or both; and (third) the stipulated term for both or either of them.
Uncertainty in the contract itself is exemplified by the Prophet’s prohibition, peace and blessings be upon him, of two sales in one sale, a sale with a forfeitable deposit, and the pebble sale according to one of its two interpretations. The same applies to similar transactions in which neither the price nor the item sold is unknown, but uncertainty arises because the parties conclude the contract on such terms.
Combining goods sold by measure and goods sold without measurement in a single transaction falls into this category. To understand which combinations are permissible, one must recognize that some goods are ordinarily sold by measure but may be sold without measurement, such as grain; others are ordinarily sold without measurement but may be sold by measure, such as land and cloth; and still others are commodities that may not be sold by measure or weight, such as slaves and livestock.
It is agreed that goods sold without measurement which are ordinarily sold by measure, such as grain, may not be combined in a single sale with a measured quantity of the same kind, nor with a measured quantity of goods ordinarily sold without measurement, such as land and cloth. Likewise, it is agreed that goods sold without measurement which are ordinarily sold in that manner may not be combined with a measured quantity of the same kind,