What is the precise definition of "counted," "measured by volume," and "weighed" items, along with examples for each, and do the Shar'i rulings related to commodities change if their state changes, such as sheep becoming weighed in our time?

Quantities are of four types: measure by volume (كيل), measure by weight (وزن), measure by length (ذرع), and measure by count (عدد), each having ancient and modern units of measurement.

The rulings concerning transactions related to quantifiable items may vary according to prevailing customs in their estimation. This is due to the relationship between the Shariah ruling and the original ancient estimation of these quantities, which falls into three categories: 1. The ruling is tied to the original estimation due to a specific characteristic within it: The ruling does not change regardless of how the estimation changes, such as equivalence by volume in the exchange of usurious commodities measured by volume, like dates. 2. The ruling is tied to the original estimation for a purpose that can be achieved by any suitable estimation: The ruling does not change, such as the unrestricted sale of quantifiable items, where it is permissible to sell an item measured by volume by weight, or an item measured by weight by volume, as long as the condition of knowing the sold item is met. 3. The ruling is tied to the original estimation because it is the customary estimation: The transaction is valid with it as long as people customarily agree upon it, such as a loan of quantifiable items that are returned in kind based on the customary estimation.

As for the sale of sheep, they are sold by count (by head) and not by weight, and their price is estimated by their weight. There is no harm in this. Regarding the issue of possession, it is not permissible to sell a flock until it has been counted.