Thursday 17 October 2019



Rabbi Aryeh Kaplan (1934-1983) was a nuclear physicist and a highly respected rabbi who authored over fifty books. Although he passed away at the untimely age of 48, during his short life he managed to get listed in the Who’s Who in Physics, was credited with being a major player in the Baal Teshuvah Movement, and he revived and reconstructed ancient Jewish meditation practices from original texts.

His scholarly books speak for themselves and his authority is widely recognized.

In this article, however, we will take a look at the even more fascinating human being behind and beyond the books.


Aryeh Moshe was born Leonard Martin in the East Bronx in 1934 to non-religious parents, Samuel and Fannie Kaplan. His mother passed away when Leonard was only 13 years old, and his sisters, Sandra and Barbra, were sent to a foster home.

Leonard, or Len as he was known, was expelled from a public school in the Bronx and became a street kid.

On one occasion, the young Len saved a Chassidic boy of about his age from being attacked by a gang. This lad, Henoch Rosenberg happened to be a Klausenburger Chassid and he encouraged his new friend to say Kaddish for his mother and he started to teach him Chumash. Apparently, Len then joined the Klausenburg Yeshiva and became close to the rebbe, who later suggested - after some time at Yeshiva Torah Vodaas and Mir Yeshiva in Brooklyn - that he go and further his studies in Israel.

Len then became Aryeh and he enrolled at Mir Yeshiva in Jerusalem. In 1956, he received his rabbinical ordination from Chief Rabbi Yitzchak Hertzog and also from R. Eliezer Yehudah Finkel, Rosh Yeshiva of Mir.

In the late 1950’s R. Kaplan returned to America and began his secular studies in various universities where he excelled at physics and emerged a Nuclear Physicist.

A sample of  R. Aryeh Kaplan's secular work.

Then, in the mid-1960’s he decided to go back to his first love and to seek work as a rabbi.


The following extract is from his 1956 ordination certificate issued by the Mir Rosh Yeshiva:

“I have the opportunity to recognize the honor of Rav Aryeh Moshe Eliyahu Kaplan from Brooklyn, New York...[who has] merited to good name and is well-known as a genius, an expert in Shas, Rishonim, Acharonim, and for all laws to be given Yoreh Yoreh Yadin Yadin.
And that it will be that he’ll be one of the great of our generation and that many will come to the light of his Torah and fortunate is the congregation that will have him as a rabbi and teacher.”

The ‘fortunate congregations’ he served at are surprisingly interesting:

From the Globe-Gazette, page 8, Mason City 1965.

From 1966 to 1967, R. Kaplan became the rabbi of B’nai Shalom, a Conservative synagogue in Tennessee.

From 1967 to 1969, he serves at Adath Israel, a Conservative synagogue in New Jersey.

From 1969 to 1971 he moved to Albany where he presided over Ohav Shalom, again a Conservative synagogue.

According to Dr Alan Brill[1]:

He seems to have done quite a few weddings jointly with Reform and Conservative clergy.”


A strong influence in R. Kaplan’s life was R. Tvi Aryeh Rosenfeld (d. 1978) who pioneered the spreading of Breslov teachings in America and throughout the English speaking world. The two partnered together on a number of Breslover publications. This was at a time when, unlike today, very few had even heard of the name Breslov.

[On a personal note, my teacher R. Chaim Kramer told me how he sat together with R. Kaplan as youngsters at the shiurim of R. Rosenfelt, and how he remembers R. Kaplan writing meticulously in minuscule handwriting, filling volumes onto a single page. R. Kramer eventually married R. Rosenfelt’s daughter and went on to found the Breslov Research Institute and he and R. Kaplan continued to work together on other projects. See The Sweeter Side of Breslov.]


R. Kaplan was not in the least hesitant to actively participate in interfaith events, and boldly expressed his views on the subject of faith.

According to the Mason City Globe Gazette in 1966:

“St. John’s Episcopal Church Sunday night became the first Episcopal Church in the state reported as electing two women to its vestry...

In the general annual meeting which followed a potluck meal, the group heard Rabbi Leonard M Kaplan of Adas Israel Synagogue say: ‘We often spend much effort in making a god out of our particular religion. Shouldn’t we spend just as much effort in making our religion a religion of God?’

Rabbi Kaplan called for efforts to appreciate strange and often exotic religions, understanding that each one speaks for God and may even have a message for us...

‘In a sense, every religion is an open eye upon God, giving us its own flat, one-dimensional view...It is only the totality of them all that can give us a multidimensional view of the Divine and a panorama of infinite depth...

The eye does not hate the ear for not seeing. The ear does not despise the nose for not hearing. The many religions perceive God, each in a different way. But as long as they all look toward God, they are one.’


In the early 1980s, R. Kaplan was a rabbinic consultant for the movie Yentl. Years ago, when I saw that movie, I remember thinking that it was unusually accurate in its depiction of religious Jews – now I know why:

“Rabbi Leonard Kaplan enjoyed advising the cast on ritual and its meaning. He showed them how to sway and bend while they pray, explained what it means to study the Talmud and in general helped the cast understand the outlook of a religious Jew.”

The movie is about a girl who dresses up as a boy so that he/she could study Talmud. R. Kaplan was quite comfortable in his role as a consultant in such an unusual movie because, as he said, even if “It is an what?


R. Kaplan was concerned about whether it was permissible to invite people to services on Shabbat if it was probable that they would drive to the synagogue. He wrote to R. Moshe Feinstein who subsequently addressed the following responsum[2] to R. Kaplan:

R. Moshe Feinstein essentially said:

“...Regarding the matter of making a service...even for young people under Bar Mitzvah, who will definitely arrive by motor vehicles because of the long distances [they would have to travel to the synagogue] and thereby desecrate the Shabbat – it is simple and clear that it is forbidden...”[3]

According to R. Ari Kahn:

 “...based on the other rabbinic positions he takes – notably Iowa – which...only had ‘late’ Friday night services, it would seem that he [i.e. Rabbi Kaplan][4] did not accept Rav Moshe’s psak.”[5]


In 1971 R. Kaplan moved to Brooklyn where he remained until his passing in 1983 but he never took a position of rabbi again. He settled in the outskirts of Boro Park.

Perle Besserman[6] describes how, during the late seventies, R. Kaplan’s living room was a sort of centre for gatherings, which attracted, amongst others, such diverse crowds as modern orthodox psychologists; Jews who had just returned from India; as well as those “ who just crashed on his couch.”

Shaul Magid writes[7] that:

“Kaplan’s decision to live on the margins of Boro Park was more than symbolic...Kaplan decided to stay on the margins of that world.”

His books on Kabbalah had been printed by a New Age press in Maine and this apparently “bothered some of the more conformist haredim in Boro Park...


Shaul Magid describes R. Kaplan’s phase as a painter:

“His dining room was adorned with a series of bizarre oil paintings. At some point, with no training as an artist, Kaplan decided to refrain from study for a year and devoted himself to painting. After the year he stopped and never painted again.”


Although many believe the world to be close to six thousand years old (starting from the first Shabbat), R. Kaplan took the position that the Big Bang occurred “approximately 15 billion years ago.” This, he said corresponded to the views of the 13th century Kabbalists, and to the views of other rabbinic sources. He presented a paper on this matter to the Association of Orthodox Jewish Scientists.

(According to ESA’s Planck project of 2015, the age of the universe was set at 13,799 +/- 0.021 billion years.)


R. Kaplan wrote that some medieval Kabbalists may have used psychedelic drugs[8] to achieve lofty states. Also, cannabis, known as k’nei bosem (sounds similar) was used in the anointing oil.[9]


In a 1980 interview[10] R. Aryeh Kaplan said:

I consider The Handbook the most important thing I’ve ever done. I wrote most of it about 12 years ago. While I was writing it, I gradually realized that Jewish philosophy almost comes to an abrupt end in the 14th and 15th centuries. And from there on, almost all of Jewish philosophy and Jewish thought and theology is dominated by Kabbalah.”

R. Kaplan was able to ascertain that rationalist/philosophical thought was abruptly ended around the 1300s and that the mystical tradition thereafter dominated most of Jewish thought. This is an interesting cut-off date for those interested in the understanding of when Jews were finally weaned off rationalist thought and philosophy.


R. Kaplan appears to have believed in the possibility of extraterrestrial life. To this end, he cited a number of classical rabbinic sources including Chasdai Crescas[11] and the Kabbalisic work Sefer ha Brit[12].

He wrote that “[t]here may be other forms of intelligent life in the universe, but such forms do not have free will, and therefore do not have moral responsibility – at least in the same sense as human beings.[13]


On another personal note – not that I have strong feelings one way or the other on the subject of extraterrestrial life – but I once gave a talk and mentioned, in passing, the possibility of extraterrestrial life being compatible with some rabbinic sources as documented by R. Kaplan. The next day I received an email from an authoritative institution asking me to rather stick to ‘more conventional sources’. 

R. Kaplan and his sources, it seems, were not conventional enough. Anyway, I sent them a long list of rabbinical sources and many years have since passed but I haven’t heard back from them since.

R. Aryeh Kaplan appears to have been as normal as he was exceptional. 

It seems that he had a great sense of humour; he had hippy as well as scholarly friends; he sometimes skipped class at Yeshiva but he graduated with distinction; he once wore a toupee; he loved growing cactus plants; he researched, wrote, painted, and above all he always thought out of the box.

R. Pinchas Stolper - R. Kaplan’s original sponsor - described him, essentially, as a man who was never afraid to speak his mind. 

With a mind like his, it is no wonder that some had difficulty in keeping up with, let alone understanding him.


See here for how a complete chapter of R. Aryeh Kaplan's Handbook of Jewish Thought was censored out of his published work because it presented evolution 'as part of the basic tenets of Judaism'.

[1] The Book of Doctrines and Opinions; Lost Rabbi Aryeh Kaplan, Part II.
[2]Igrot Moshe, Orach Chaim, Siman 98.
[3] My loose translation of a short extract of the responsum.
[4] Parenthesis mine.
[5] The Book of Doctrines and Opinions; Lost Rabbi Aryeh Kaplan, Part III.
[6] Pilgrimage: Adventures of a Wandering Jew
[7] Piety and Rebellion: Essays in Hasidism, by Shaul Magid.
[8] Meditation and Kabbalah, by Aryeh Kaplan, p. 156.
[9] The Living Torah, Aryeh Kaplan, p. 442. 
[10] Conversations in the Spirit: Rabbi Aryeh Kaplan.
[11] Or haShem 4:2.
[12] By R. Pinchas Eliyahu Horowitz.
[13] The Aryeh Kaplan Reader: On Extraterrestrial Life.


  1. Really loved reading this. Have read many of his books and he was able to explain a deep concept in a simple way.

  2. הדת תשים משטרה על עניני הקודש, ותניח את ידה מעניני החול. זהו מושג מחוייב ממושג הדת. האלהים הוא מתגלה מן הכל, מתוך הקודש ומתוך החול.

    The religion polices matters of the holy, and abandons matters of the secular. That is essential to the idea of religion. But God is revealed from all things, from within the holy and from within the secular.

  3. Nice R. Moshe. Maybe its time to start a Kook Blog!!

  4. it would be nice if someone would mention his sefardic roots. He has translated the Meam Loez from its original ladino. see his introduction there.

  5. Are you sure that first photo is of Aryeh Kaplan?
    Fave isn’t as round, lips thinner than in the photo in the newspaper clipping, no noticeable dimple in chin in the second photo either. Could be just the poor reproduction, but I am suspicious. Thanks for posting this short biography of an extraordinary man.

  6. I was close to Reb Aryeh and spent a great deal of time in his home. He NEVER bragged and was loath to receive a compliment however I recall that I was once sitting next to him at the Shabbes table and he leaned over towards me and whispered in my ear: "You know, I learned very close wit the Kloisenberger."

  7. The photo leading the essay is NOT a young Aryeh Kaplan but rather Gregory Kaplan, a Jewish Studies scholar. This photo should be removed. Thanks.

  8. Thank you for that. There were some questions raised about the photo.

    My own picture was the official Wikipedia photo depicting the Kotzker I know about mistaken identity.