Insights into Halacha

For the week ending 4 February 2012 / 10 Shevat 5772

Leeuwenhoek's Halachic Legacy

by Rabbi Yehuda Spitz
The Color of HeavenArtscroll

Antonie van Leeuwenhoek (1632 - 1723), although not the developer of the first rudimentary microscope, nonetheless is the figure most closely associated with the microscope’s mystique. He is credited with discovering micro-organisms, and is considered the greatest contributor toward making the microscope the essential research tool that it is known as, even today. In fact, his designs for improving the microscope were not successfully replicated until 1957, over two hundred years after his death!

Although the scientific, research, and medical significance and benefits of Leeuwenhoek’s work are obvious, this article sets out to explore what halachic relevance his innovations have.

This issue actually affects many different aspects of halacha, the foremost being what status something that can only be seen with a microscope has in Judaism. For example, at Sukkos time everyone checks their esrogim for blemishes. What is the status of an esrog that has no noticeable blemish, but, when viewed under magnification glass, loupe or microscope, one can perceive imperfections? Similarly, if one can ascertain a problem in the script of a Sefer Torah only via a magnifier, would that invalidate the Sefer Torah? The most common question though, arises when checking produce for insects[1]. If one cannot detect any sign of bugs in the produce, but they may perhaps be visible through magnification, is one allowed to eat the produce? And if not, is one required to use such a magnifying device to check to ensure that there are no lurking insects?

This issue, although a recurring theme in Judaism, is not a new one; it was already addressed hundreds of years ago. There is a minority opinion that if a magnifying glass can help to better find insects one would be required to use it to do a proper thorough inspection[2]. However, the majority of late Acharonim, including such luminaries as Rav Shlomo Kluger[3], the Chochmas Adam[4], the Tiferes Yisrael[5], and the Aruch Hashulchan[6], emphatically statethat the Torah would not require something that could not have been kept at all times. As such, a magnifying glass or microscope could not possibly have been mandated for a halachic inspection, as it has only been around for several hundred years. Additionally, when the Torah commands an inspection, it must be something that the average Joe can personally perform[7], without the aid of instruments.

These authorities cite several proofs of this from diverse Biblical passages, such as the passage dealing with a Nazir[8], to whom all wine and wine byproducts (including wine vinegar) are prohibited, and by Ruth[9], who was told by the greatest authority of the time to dip her bread in vinegar. Yet, nowhere do we find that they pulled out a magnifying glass to check the vinegar (which was one product that over the millennia had a high infestation rate) to ascertain that no microscopic insect might have been inside. Furthermore, if minuscule mites would be prohibited due to the ability to see them under a microscope, how can anyone breathe? Every time we inhale we would be ingesting thousands of infinitesimal insects! The Torah was given to people, not angels!

The vast majority of contemporary authorities, almost without exception (!), rule this way as well, that re’eeyah - seeing - can only be referring to natural G-d-given eyesight, and any magnifying tool will not change the halachic status of whatever needs to be checked[10], whether an esrog, tefillin, Sefer Torah or flour.

However, as mentioned in a previous article, “Bubby Didn’t Eat Bugs”, there are those who opine that it might be worthwhile to use a magnifier to help check better if one can already see something, but is unsure what he is seeing. For example, if one can see a black dot, these authorities feel that one should use a magnifying glass to ascertain if it is an actual insect or merely dirt[11]. As stated previously, not everyone agrees with this though[12]. Another application of this concept is to familiarize yourself with what you are seeing, i.e. checking lettuce by using the magnifier, as it is entirely possible that you are really seeing an insect, but don’t realize it as it might be camouflaged. Once one checks with magnification, he will recognize what the bugs look like and will be able to see them without visual aid[13].

But the bottom line is that using a magnifier or microscope to see something that cannot be seen by the naked eye would have no halachic bearing “bein lehakel bein lehachmir”. So, although Leeuwenhoek’s impact on the world in various important areas is immeasurable, nevertheless, his halachic legacy remains, interestingly, microscopic.



[1]See earlier article “Bubby Didn’t Eat Bugs!”.

[2]The Ya’avetz (Shu”t Sheilas Ya’avetz vol. 2, 124) and the Sefer HaBris (cited in Binas Adam 38) imply this way. Rabbi M.M. Weissmandl in article in Kovetz Ohr Yisrael (vol. 20) opines that there is no real argument and differentiates between a magnifying glass and microscope. However, the actual words of the authorities do not make this distinction and it would seem would maintain that neither would make a halachic difference.

[3]Shu”t Tuv Ta’am V’Daas (Tinyana, kuntress acharon, 53), who vehemently objects to the Ya’avetz’s words.

[4]Binas Adam (34, to klal 38), who rejects the words of the Sefer HaBris.

[5]Tiferes Yisrael on Maseches Avoda Zarah (Ch.2 Mishna 6, Boaz 3).

[6]Aruch Hashulchan (Y”D 84, 36).

[7]Several authorities stress that the halacha is referring to people with good eyesight (20/20 vision). See Shu”t Chasam Sofer (O.C. 132 s.v.v’odos) and Darchei Teshuva (84, 15).

[8]Bamidbar (Parshas Nasso Ch.6, verse 3).

[9]Ruth (Ch. 2, verse 14).

[10]Including Rav Chaim Soloveitchik of Brisk (cited in Shu”t Igros Moshe Y”d vol. 2, 146 s.v. umah), the Melamed L’hoyeel (Shu”t vol. 2 Y”D 27), the Chazon Ish (cited in many sefarim including Orchos Rabbeinu vol. 3, haghos to O.C., hilchos tefillin 12; Maaseh Ish vol. 1,pg. 20; Nezer Chaim pg. 375, klalim nifradim 1), the Steipler Gaon (Kraina D’Igresa vol. 2, 77), Rav Moshe Feinstein (ibid and E.H. vol. 3, 33 s.v. aval and Y”D vol. 4, 2), the Tchebiner Rebbe (Shu”t Dovev Meisharim vol. 1, 1), Rav Shlomo Zalman Auerbach (Shu”t Minchas Shlomo, Tinyana 63, 2 s.v. uma’attah and Halichos Shlomo Moadim vol. 2, Pesach Ch. 7, 25), the Debreciner Rebbe (Shu”t Ba’er Moshe vol. 5, 16), Rav Yosef Shalom Elyashiv (cited in Ashrei HaIsh vol. 3, pg. 211 end 13), Rav Shmuel HaLevi Wosner (Shu”t Shevet HaLevi vol. 7, 2, 10), Rav Moshe Sternbuch (vol. 1, 628 & vol. 3, 323), Rav Ovadiah Yosef (Shu”t Yabea Omer vol. 4, Y”D 21, 7 & Shu”t Yechaveh Daas vol. 6, 47), the Pri Chaim (Shu”t Y”D 43), the Bais Avi (vol. 1 O.C. 64), the Mayim Chaim (Shu”t O.C. 259), the She’arim Metzuyanim B’Halacha (46, 16 and 20), and the Yalkut Yosef (IV”H vol. 2, 84, 6). And although the Shearis Yisrael (vol. 1, O.C. 11 & 12) argues on the Dovev Mesharim and Chazon Ish by a certain specific case, see Shu”t L’Horos Nosson (vol. 5, 2, 2) who explains that he only disagrees by that specific case but the rule hold true. Similarly, although Rav Dovid Baharan (brought in the Kuntress Bein Hashmashos of the Even Ha’Ezel) cites a proof from the Gemara in Bechoros 52b that the Torah can be referring to supernatural eyesight, the Even Ha’Ezel himself (vol. 8, hilchos Krias Shma Ch. 1, 3 s.v. v’henei harav) dispels his proof, and maintains that this ruling holds true.

[11]This is essentially a dispute between Rashi (Eiruvin 28a s.v. tzirah, Chullin 67b s.v. b’aviha) and the Rashba (Shu”t vol. 1, 275) whether one needs to ascertain actual movement of the dot, or one has to assume that it is a bug. On this topic see Rema Y”D 84, 6; Shach (ad loc 20), Minchas Yaakov (46, 7), Pri Megadim (ad loc S.D. 20), Chochmas Adam (38, 9), Shu”t Beis Efraim (Hachadashos pg. 8), Shu”t Tzemach Tzedek (Hachadashos Y”D 92, inthe brackets), Mishmeres Shalom (84 S.D. 8, 2, citing the Maharsham), Darchei Teshuva (84, 28 s.v. Ayi”sh), and Kitzur Shulchan Aruch (46, 34). The Chazon Ish (above) was known to have ruled stringently with this.

[12]See for example, Shu"t Shevet HaLevi (vol. 7, 122), Shmiras Shabbos K'Hilchasa (Ch. 3, 37, 105), Halichos Shlomo - Tefilla (Ch. 4, 25, 78), V’Aleihu Lo Yibol (vol. 2, Y”D 1), Shu”t Igros Moshe (Y”D vol. 2, 146 s.v. umah & Y”D vol. 4, 2), and Yalkut Yosef (IV”H vol. 2, 84, 21).

[13]Shu”t Machazeh Eliyahu (91, 8). He brings proof of this from the Chasam Sofer’s custom (Minhagei Chasam Sofer Ch. 10, 18; see also Shu”t Chasam Sofer Y”D 277) on Erev Pesach by checking Maror.


For any questions, comments or for the full Mareh Mekomos / sources, please email the author: yspitz@ohr.edu

Disclaimer: These are just a few basic guidelines and overview of the Halacha discussed in this article. This is by no means a complete comprehensive authoritative guide, but rather a brief summary to raise awareness of the issue. One should not compare similar cases in order to rules in any real case, but should refer his questions to a competent Halachic authority.


Disclaimer: This is not a comprehensive guide, rather a brief summary to raise awareness of the issues. In any real case one should ask a competent Halachic authority.


L'iluy Nishmas the Rosh HaYeshiva - Rav Chonoh Menachem Mendel ben R' Yechezkel Shraga, Rav Yaakov Yeshaya ben R' Boruch Yehuda, and l'zchus for Shira Yaffa bas Rochel Miriam and her children for a yeshua teikef u'miyad!

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