When the Torah goes out of its way TB Pesakhim 18

As we have learned there are four things that can become susceptible to tumah (טומאה) and they are: humans, utensils (כלי), food, and liquids. Previously we been discussing the opinions whether liquids can transmit tumah at all, according to the Torah law, or only according to rabbinic decree. Today’s daf TB Pesakhim 18 reaffirms several halakhot when it comes to tumah and taharah (טהרה). Only an av hatumah can make a utensil tamei or ritually unready. Ritual unreadiness cannot render a similar item ritually unready. For example liquid that is tamei cannot render other liquids tamei.

What can contaminates what are derived from rabbinic interpretation of verses. One method is the kal vehomer (קל וחומר) or a fortiori inference. “The most basic hermeneutical methodology is the kal v’chomer, known in Latin as an argument a fortiori, meaning “from the stronger case.” The nature of an argument a fortiori is “Arnold is known to be stronger than Barack. If Barack can lift 100 lbs., a fortiori Arnold can lift 100 lbs.” There is a limit to the argument a fortiori, however: you can’t get more out of it than you put into it. So, I may know that Arnold is stronger than Barack, but I don’t know if that means Arnold can lift 200 lbs., 150 lbs., 101 lbs. or 100 lbs. and 1 oz. All I know for sure is that Arnold can certainly lift whatever Barack can lift.” (https://outorah.org/p/6495/)

A basic rabbinic principal is that the Torah is perfect and doesn’t even have a superfluous letter. The Gemara wonders why the Torah explicitly states the law that liquids can become tamei when it comes in contact with a utensil, a rishon letumah, when we know that it can become tamei by coming in contact with an av hatumah by a kal vehomer.

 “The Gemara asks: And let the verse teach us that liquids do not transmit impurity with regard to liquids that come to a state of impurity due to contact with a creeping animal, and all the more so will that be the case with regard to liquids that come to a state of impurity due to contact with a vessel. The Gemara answers: This is not difficult, as at times with regard to a matter that could be derived by means of an a fortiori inference, the verse nevertheless unnecessarily wrote it explicitly.” (Sefaria.org translation)

 Most of the commentators teach that there is a difference when a law is taught by a kal vehomer or the Torah goes out of its way to explicitly teach it with a verse. When there is an explicit verse in the Torah we must act more stringently in its implementation because the Torah emphasizes its importance with a verse. (Tosefot, Rabbi Yehuda HaLevi Mintz)