Taharos, Chapter 9, Mishnah 9. Our chapter has been tracking olives through the stages of their preparation and asking how tumah moves through them. This Mishnah continues with a sheretz that has been discovered somewhere in the olive press, and it closes with one of the great governing rules of the entire masechta: we judge tumah exactly as we found it, and we do not extend it by speculation.
A heap and loose fragments
"Nimtza al gabei perudim vehu noge'a kekhabeitzah, tamei": the sheretz was found resting on separated olive fragments that were gathered into a heap, and it is in contact with the volume of a kabeitzah. The whole heap is tamei. A heap counts as a single unit, so contact with a kabeitzah's worth of it draws all of it in. This is the opposite of individual crushed olive particles lying loose, which are each too small to hand tumah on to the next one.
Next comes "Perudim al gabei perudim", separated bits lying upon other separated bits. Here, even if the sheretz makes contact with an egg's volume of them, the ruling is "ein tamei ela mekom maga'o": nothing becomes tamei beyond the precise point of contact. Nothing in this arrangement has been consolidated into one body. Small pieces have simply been piled over small pieces, and halachically every piece stands as its own separate item.
Lodged against the wall
"Nimtza bein kotel lazeitim, tahor": the sheretz turned up in the gap that separates the wall from the pile of olives, meaning that it is touching no olive at all. The olives retain their taharah. It would be tempting to argue that the creature had surely been sitting somewhere among the olives earlier and only afterward worked its way out to the spot where we now see it. Halachah refuses that line of reasoning. As the Mishnah declares in its final words, a case of tumah is ruled upon according to the circumstances in which it turned up.
The vat and its roof
"Nimtza begag hama'atan, hama'atan tahor": the sheretz was found on the roof covering the ma'atan, the vat where the olives are left to soften. The vat below is tahor. We do not argue that the sheretz must have climbed out of the vat and therefore contaminated the olives inside; we take the sheretz where we found it, on the roof.
"Nimtza bema'atan, hagag tamei": but if the sheretz was found inside the vat, the roof is tamei. Here the conclusion is unavoidable, because there is no way for the sheretz to have reached the inside of the vat other than by passing over the roof. Note the precision of the two rulings together. We do not abandon plain logic where a fact is forced upon us; what we refuse to do is build tumah out of what merely might have happened, however plausible it sounds.
Burnt remains
"Nimtza saruf al hazeitim, vekhein matlis mehumam, tehorah": a sheretz was discovered already charred as it lay over the produce, and the same applies to a rag that had once carried tumah and has since been scorched away. In both situations the olives retain their taharah. Whatever we are looking at has ceased to be a metamei: the fire has destroyed the sheretz, and the remnant of cloth has been consumed. We are not asked to trace matters backward and imagine what these items were once able to transmit before they met the flames.
The closing principle
"Shekol hatumos kish'as metzi'asan": all cases of tumah are judged according to the moment of their discovery. This is the thread running through every ruling in the Mishnah. We evaluate what is in front of us as we find it, we accept what logic compels, and we do not project tumah backward into a history we did not witness.