I've noticed that some people, when reciting kaddish, pronounce the first words as "yisgadal v'yiskadash" with a patach under the dalet of both words, while others say "yisgadel v'yisgadesh" with a tzere. The siddurim that I own are in accordance with the former practice.
Is one version more correct than the other, and if so, which? And what is the origin of the incorrect version?
The short answer is that modern yeshiva students recite it with a tzeirei because this is brought in the Mishna Berura which has become a very popular sefer for "p'sak". The Mishna Berura brought it because of the weight he gives to the Pri Megadim, who quotes this version in the name of R' Hanau.
A more interesting and comprehensive background with sources can be found here.
While I have not read it myself, "The Kaddish" by David de Sola Pool came highly recommended to me by a leading scholar in the study of Aramaic when I posed the same question to him a few years ago. (This question has reminded me that I am very far behind on my reading list.)
This scholar's response to my question at the time was, in a nutshell, that the former seems to be the most "correct". As an added bonus, part of my question to him was centered around the point that there is a Yod that, if my Babylonian Aramaic class in college taught me anything, ought to be a Lamed. He responded that it is written in Geonic Aramaic, which has some deviations from Babylonian Aramaic of other periods.
Unfortunately, without his consent to quote him and broadcast his opinion throughout the interwebs, I feel I must withhold the identity of this scholar from the broader audience. But if he recommended a book on the subject, I feel confident recommending it to the community.
Rav Moshe Heinemann says in Mah Nomar Tefillah:
Q. Should one say Yisgadal v’Yiskadash or Yisgadeil v’Yiskadeish?
A: This is a dikduk question. Yisgadal v’Yiskadash is Hebrew and Yisgadeil v’Yiskadeish is Aramaic. The question is: do you start this Kaddish in Aramaic since the rest of the Kaddish appears to be Aramaic or are you supposed to start Kaddish in Hebrew? Some medakdekim say that you could say Yisgadal v’Yiskadash even in Aramaic and some say you could Yisgadeil v’Yiskadeish in Hebrew. I want to tell you a story that happened with the Rosh Yeshiva here, Rav Ruderman zecher tzaddik l’vracha, when he had yahrzeit. In his last years b’sof yamav, he did not daven from the amud when he had yahrzeit. He used to make Rav Moshe Mintz zol zein gezunt a shliach to daven for whatever reason. When Rav Ruderman was younger, he did daven from the amud and after davening Mincha Chazaras hashatz he said Yisgadeil v’Yiskadeish, which was the minhag in most Litvishe Yeshivos, but then after Aleinu he said Yisgadal v’Yiskadash. I asked him which one is the right thing to say, and he said he was mesupak about it, which is why he said it in different ways in order to be yotzei either way. There is no real right or wrong way about this. I believe that most places say Yisgadal v’Yiskadash, and it seems that the minhag in Slobodka was to say Yisgadeil v’Yiskadeish. Whatever you do, you are yotzei the Kaddish.
In the footnote he quotes the Mishna Berura (56:2) - הקדיש - נוסח הקדיש יתגדל ויתקדש שהוסד ע"פ המקרא והתגדלתי והתקדשתי האמור (ביחזקאל לח:כג) לענין מלחמת גוג ומגוג שאז יתגדל שמו של הקב"ה דכתיב ביום ההוא יהיה ד' אחד ושמו אחד. ויאמר הדלית דיתגדל ויתקדש בצירי כי הוא עברי ולא תרגום [עיין בב"י] ולא בשני שוואין כאלו התיו והגימל בשווא אלא הגימל בפתח. וידגיש הגימל דיתגדל דלא לישתמע יתקדל לשון עורף תרגום עורף קדל. ולא ידגיש ביותר הב' דיתברך
Mishna Berura writes (56:2) that the correct pronunciation is with a Tzeirei צירי, making it "yisgadeil v'yiskadeish."
The reason he gives for that is that even though kaddish is in Aramaic (which would imply yisgadal, apparently), these two words are meant to be in Hebrew. This phrase is based on a verse (Yechezkel 38:23), which uses the phrase "והתגדלתי והתקדשתי" in the context of the end of days, which is the subject of kaddish.
