I am looking to coin the above title into yet another Latin phrase, because of late I have identified it as another fallacy not employed in the Maimonidean and Vilnian systems. Examples: The fact that certain communities refrain from eating cooked rice and beans, etc., on Passover does not turn those cooked rice and beans into prohibited substances. Cases in point: Those who subscribe to the fallacy would prohibit cooking rice in one’s Passover pots for consumption right before and right after Passover, whereas those who restrict the rule to its simple meaning, “we refrain from eating such things on Passover,” would allow cooking the rice in Passover pots. This came up once again this year, when the Sabbath immediately followed Passover. As we have seen, the great Ashkenazic authorities, despite the fact that did not eat cooked qitniyoth Passover, did not relate to qitniyoth as prohibited substances.
Second case in point: Not cutting one’s hair until Lag Ba’omer, or not getting married until then. Those who subscribe to the fallacy would be astonished by various permissibilities, for example to trim one’s beard or shave on Friday in honor of the Sabbath, or to groom oneself as part of the Independence Day celebrations, because doing so is “forbidden” during the Omer, while others realize that the custom is to not do so, but that does not mean that which is not done is inherently prohibited.
This idea has many more applications. It behooves any scholar consulted in matters of halacha to know how to distinguish between true prohibition, whether by force of neder, or by rabbinical injunction, or by Torah commandment, and customs to refrain, abstain, or avoid, for which there are, by necessity, many more leniencies.