«كل كاتب متحرك الأصابع بالضرورة ما دام كاتبا»
Every person writing is necessarily moving their fingers so long as they are writing.
The example concerns handwriting, with writer considered in the active condition of writing. Once the act ceases, the qualification underlying this particular necessity no longer obtains.
Effect of the condition: the person may continue to exist although the descriptive state ends. It would therefore be incorrect to infer “their fingers must always be moving.” The judgment applies only while writing.