By way of example, the Mishha and in turn the Gemera record various practices when a person is an אבל (mourner). One such practice is עטיפת הראש winding or wrapping of the head. Tosefot, however, note that although this practice is recorded without controversy – in their time, as it was uncommon to wrap one’s head there is no longer an obligation to do so.
At the time Tosefot offered this decision – a decision which took into account then modern sensibilities – it was fairly unremarkable. This would change significantly when a movement sprung up which took conforming Judaism to modernity to the extreme. The Reform movement which altered numerous, significant practices precipitated a greater hesitancy to effect change – even legitimate change within Orthodoxy.
One example of the battle over changing long established practices relates to Hol haMo’ad. The Mishna in Mo’ad Koton  enumerates but a small class of people who are permitted to shave on Hol haMoad. This class is comprised of people, who for reasons out of their control were unable to shave before the holiday. One who is released from prison on the Holiday is one example. But, anyone other than this small class of persons according to the Mishna, are prohibited from shaving on Hol haMo'ad. The Gemera explains the restriction in light of human nature. One, in theory, has more free time on Hol HaMo'ad (assuming one is not working) thus one may procrastinate to shave and get a haircut until Hol HaMo'ad. This would mean that they would begin the holiday unkempt, unshaven. Thus, to avoid this sort of procrastination, one is prohibited from shaving on Hol haMo'ad thus removing any temptation to delay until Hol HaMo'ad.
The question which we will now turn out focus to – is whether this reason is dispositive. That is, assuming one did in fact shave before the holiday can he then shave on Hol HaMo’ad as he did comply with the law.
For hundreds of years the answer to this question was no. Rabbenu Tam (1100-1171) did allow for someone who shaved before the holiday to do so on hol haMoad. This position, however, was uniformly rejected by everyone who voiced an opinion on this matter until the 18th century. The 18th century, however, saw an increase in emancipation and closer contact between Jews and non-Jews. This was on an unprecedented level, Jews did not want to appear strange and thus many Jews began, what is common today, dressing in contemporary style and the like. Jews also, although there were also examples earlier, began to appear clean shaven. Now, during the rest of the year, maintaining a clean shaven look did not pose too significant of a problem. But, there was one time where, based upon precedent, it would be difficult to remain clean shaven – during Hol HaMo'ad.
The first to readdress this issue was R. Yehezikel Landau, the author of the Noda B’Yehuda and one of the greatest Rabbis of his time. In approximately, 1775, R. Landua was asked (O.C. Tinyaha, no. 101) if there was any way for those who shave year round, and did so prior to the holiday, to do so on Hol HaMo'ad. R. Landau ruled in the affirmative, with one important condition – that it be done with a poor barber. This condition was an attempt to conform with the various prior opinions. Namely, R. Landau understood the rejection of Rabbenu Tam’s opinion limited to instances which the person would shave themselves. But, a poor person who needed this to survive and thus was able to do work on Hol HaMo'ad anyways, everyone would agree shaving would be permitted. As R. Landau was highly respected his opinion did not go unnoticed. With the publication of this responsa in his work Noda B’Yehuda, the reaction was almost immediate and negative. From all over Europe various people either directly addressed R. Landau or wrote their own private responses expressing their opinion to maintain the status quo. In the end, R. Landau included four responsa on this topic. The reaction was summed up by R. Hayim Yosef Azulai, the Hida (Yosef Ometz, no. 7),
ואולם בו בפרק ראיתי אשר תיכף אזרו חיל הגאונים רב של ברלין ורב של אמשטרדם וחלקו עליו, ונדפס בספר בינן אריאל. גם ידעתי נאמנה שרבני גאוני פולין ואשכנז היטב חרה להם היתר זה וכמעט נגעו בכבוד הרב. ואין ספק כי רבני ארץ ישראל . . וכל טורקיאה ומצרים . . . וערי המערב . . . כולם יסמכו עם רבני אשכנז ופולין“During that time I heard immediately they quickly girded themselves, the great ones, the Rabbi of Berlin, the Rabbi of Amsterdam and they disagreed [with R. Landau] and this was printed in Binyan Areiel. I also heard from trustworthy sources that the Rabbis of Poland and Germany were extremely disturbed by this leniency and they went so far as to disparage R. Landau. And I have no doubt that the Rabbis in Israel, Turkey, Egypt, and all the Eastern lands agree with the Rabbis of Poland and Germany.”
There were those, who could not reconcile their high esteem of R. Landau with his permissive stance on shaving, and thus made the claim (which has no support) that R. Landau retracted his statement. [Such a claim - that the author retracted or an errant student was the author of a controversial respona - is rather common. See Speigel, cited below, pp. 271-75 for other examples.]
One particularly fantastic (and well-known) explanation attempting to reconcile the R. Landau’s position was offered by R. Moshe Sofer, the author of Hatam Sofer. R. Sofer (Shu"t Hatam Sofer O.C. no. 154) wants to understand R. Landau’s position in light of another shaving question. One is prohibited from using a straight edge razor on their face. But, as this was before electric shavers many of the other options for shaving were not appealing to some and they used a straightedge anyways. R. Landau was offered a possible justification for this practice, which R. Landau in turn rejected. The justification was one is prohibited from removing “hair” with a straight edge. Hair is only hair, for many other laws, if it is long enough to turn back on itself. Thus, if one shaved every day or so, even with a straightedge they would not be removing hair as it was too short. Now, as I mentioned R. Landau rejected this, however, R. Sofer claims as this position was perhaps the only available understanding of what many did to not consider them sinners, R. Landau in fact accepted this. But, R. Landau also knew that if he came out that shaving was prohibited on Hol HaMo'ad many people even those who use a straightedge will follow that opinion. Thus, at the end of the holiday they would have long enough facial hair to be shaving “hair.” While ascribing such motivation to R. Landau is somewhat far-fetched, it does demonstrate how far people would go to reconcile their views of R. Landau with this position.
This, as would be expected was not the end of this issue. Soon after the Noda B’Yehuda was published, another book – which was controversial in its entirety – was published. This book, Besamim Rosh, (previous discussions here) was published in 1793 but attributed to R. Asher b. Yehiel who lived at the end of the thirteenth and beginning of the fourteenth centuries. Almost immediately after its publication there were those who questioned this attribution and instead said it was not the RoSH who wrote this but instead it was the publisher, R. Saul Berlin. Although there were many controversial statements in this book, R. Saul Berlin retracted only one – his statement regarding shaving on Hol HaMo’ad (no. 40). This was the only pronouncement R. Saul agreed was not from the RoSH.
Thus far, this discussion was limited to single or a few responsa, however, in the 19th century we have the battle of the books. Isaac Samuel Reggio (1784-1855) (mentioned previously here), an Italian Rabbi and admitted maskil, devoted an entire work, Ma’amar HiTeglachat (Vienna, 1835), to the issue of shaving on Hol HaMoad. Reggio was one of the most accomplished Rabbis of his day, he was fluent in numerous languages, founded the Rabbinic Seminary in Padua and was an amazingly prolific writer (and he also went clean-shaven as is evidenced by the portrait accompanying the article on him in the Jewish Encyclopedia here). Perhaps his most accessible book is a translation in Italian and commentary in Hebrew (titled Torat HaElokim, Vienna, 1818)of the bible based upon the simple meaning (pehsat)was recently reprinted. [It appears the sponsor of this reprint was unaware of Reggio's maskilik leanings and - as the story was related to me - was horrified to find this out and thus this edition is now difficult to obtain.]
Reggio takes the position of R. Landau one step further. You will recall that R. Landau allowed for a poor Jew to cut one’s beard but not the person himself. Reggio, however, offers that even the person themselves can shave. This is so, as he understands that in the time of the original enactment, it was highly uncommon to shave weekly and certainly daily. From this assumption Reggio notes that (1) those who shave more often the hair returns quicker and thus before it was no big deal not to shave over 8 days but today, even in such a short time the hair returns too quickly and (2) since everyone now shaves often this is not the set of circumstances the original enactment was aimed at. That is, only for those for whom shaving was infrequent was there a true fear of forgetting or pushing off shaving but today that is not nearly as much of a consideration. Of course, Reggio notes that if one did not shave prior to the holiday he can not shave on Hol HaMa'od.
This being the most sweeping ruling on this issue and the most comprehensive, an immediate reaction was not short in coming. In fact, there were two books written for the sole purpose of refuting Reggio’s position. The first, a play on Reggio’s title was Tegalachat haMa’amar (Livorno, 1839), was published anonymously. However, we now know that in fact the author was R. Avrohom Reggio, R. Yitzhak’s father!
To this day, shaving on Hol HaMoad remains a contentious issue. R. Moshe Feinstein one of the greatest American Rabbis post-Holocaust allowed for similar reasons to Reggio, one to shave on Hol HaMo'ad. R. Feinstein explains (O.C. vol. 1 no. 163) that “today for those who shave daily, they can shave on Hol HaMo'ad.” Although there is again a permissive opinion, one from a highly respected person it still did not end this issue. In the Shmerat Shabbat K’Helchata (vol. 1 p. 274), on the top portion of the text he records that it is prohibited to shave on Hol HaMo'ad. Then in a footnote he is willing to only cite to R. Feinstein’s responsa without explaining what it contains.
Additionally, in an English book devoted to the laws of Hol HaMo’ad  they have taken it one step further by judiciously quoting R. Feinstein to give a different impression than the actual respona. As is provided in this book, R. Feinstein concludes his responsa with “I only offer this permissive opinion to those who have a great need or are in pain from not shaving.” (p. 26 n. 7). This is where the quote ends in the English book [of course, this does not actually appear in the English section, rather this is all relegated to a Hebrew footnote - in the English portion, the authors only allow that if refraining from shaving would result in a loss - davar ha'avod - only then is it permitted]. But R. Feinstein actually continues with “if one wishes to rely upon my permissive stance for appearances sake only [i.e. not only for 'great need' or 'pain'] there is no need to stop him as in reality this is permitted.”
אבל מ"מ איני נוהג להתיר אלא למי שיש לו צורך ביותר או מצטער ביותר, ואם אחד ירצה לסמוך ע"ז גם בשביל היפוי לבד אין למחות בידו כי מעצם הדין הוא מותר לע"ד
Sources: The vast majority of the above comes from M. Samet article on the topic of shaving on Hol HaMo'ad. This article appears in M. Benayhu, Tegalachat B'Holo shel HaMo'ad, Jerusalem, 1995. Benayhu's book also reprints both Reggio's books as well as a significant amount of material from manuscript and he provides a history as well. Interestingly, Benayahu attempted to convince R. Shlomo Zalman Aurebach that today it would be permissable to shave on Hol HaMo'ad. Benayahu, however, notes that right when he finished this book, he was planning on showing it to R. Aurebach for his thoughts and comments but R. Aurebach passed away.
[Of course, the primary material contains additional important information]. This book is the most comprehensive discussion on the topic. Samet's article has now been reprinted in his Hadash Assur min HaTorah, Jerusalem, 2005. Samet, among other things, discusses R. Feinstein and the controversy over his opinion. There are others who discuss this topic, however, as they mainly use the two above sources (with and without attribution), and they do not add much of anything I have not provided additional citations.
I want to thank M. Solomson for providing both editorial corrections and material for this post.
 On the name of this Mescheta and whether it is Mashkim or Mo'ad Koton, see Y. S. Speigel, Amudim b'Toldot Sefer HaIvri, Kitvah v'HaTakah, pp. 326-27; 348-56 (discussing which rishonim referred to it as Mashkim and which referred to it as Mo'ad Koton and whether any conclusions can be drawn from that data).
 D. Zucker & M. Francis, Chol HaMoed, Brooklyn, NY, 1981. The book even contains an approbation from R. Feinstein, although R. Feinstein says he did not look in great detail at the book and instead his approbation is based upon the reputation of the authors.