(1) There was a shiur this past Sunday on just this question and it is on our website.

(2) I was not Zocheh yet to see the shiur but I am going to try and present some of my own answers and I apologise if I am repititious.

(3) We do possess a rule throughout the whole Torah that one follows the majority - see Shemos 23:2 "Lean after the majority" - so since one can assume that most places in Eretz Yisrael did not have an Arifah performed on them, this should mean one can be lenient everywhere.

(4) However the problem here is that there is a Halachah of "Kavu'a" - if something is in a fixed place one does not follw the majority, but we say it is 50-50. The classic example is in Kesuvos 15a, that if there are 9 stores selling Kosher meat and one store selling Tereifah meat and someone bought in one of the stores but later on cannot remember which one, he must be stringent because each store is in its fixed location and therefore the Halachah of Kavu'a makes us look at it as if there are 5 kosher and 5 Tereifah stores in town, so the questionable meat is forbidden.

Therefore in the case of the land in Eretz Yisrael also, since the fields where an Arifah was performed are in a fixed place, why do we not say that this is Kavu'a, and 50% of the land is forbidden, so we should be stringent everywhere because of a doubt in a Torah prohibition - "Safek d'Oraisa l'Chumrah"?

(5) Your question is asked by one of the Rishonim - Rabbi Shimshon of Kinon, one of the Ba'alei Tosfos - of the Tosfos school - in "Sefer Kerisus".

(6) He answers with an important principle - the Torah only gave its novel Halachah of Kavu'a if the forbidden item is in a recognizable place. In the case of the 10 meat stores, it is known clearly where the Kosher stores are, but the only problem is that the buyer cannot remember which store he bought from. In contrast one does not know at all where the place is that Arifah was ever done, so one does not say Kavu'a.

(7) The Sha'ar ha'Melech Hilchos Megilah 1:11 gives another example. He cites the Ran in Megilah 2a (in Rif pages DH u'Linyan), who writes that if one is in doubt whether a certain city was walled at the time of Yehoshua bin Nun, one follows the majority of cities which do not have such walls. The question is asked on the Ran - why not say Kavu'a and in all the cities in the world one should have to read Megilah on 15th Adar because of a doubt, and the same answer is given that one does not know at all where any of the doubtful cities are, so Kavu'a does not apply.

(8) See also Tosfos Nazir 12a DH who writes this same principle: one does not say Kavu'a when the permitted and forbidden items are not recognizable. See also Minchas Chinuch Mitzvah 531:9 who gives the above answer to your question.

(9) In summary we follow the majority of fields in the world where Arifah was never performed and Kavu'a does not apply because we have no knowledge at all of where the problematic field may be.

Kol Tuv

Dovid Bloom