K'riat HaTorah on Shabbat, Yom Tov, and fast days is followed by reading of the haftorah. The haftorah is the reading of a passage from nevi'im that has relevance to the Torah portion or to the day's occasion. R. David Avudraham, Seder Shacharit Shel Shabbat, suggests that the reason why the haftorah is read is because in earlier times there was a decree prohibiting Jews from reading the Torah. The rabbis instituted reading from nevi'im in place of reading from the Torah. Although we now read the Torah, the practice of reading from the nevi'im continues.
Levush, Orach Chaim 284:1, notes that many communities read the haftorah from the text printed in the chumashim. They do not use sifrei nevi'im that are written on parchment and follow all of the laws of writing a sefer Torah. Levush questions the validity of such a practice and states that the haftorah should be read from a text that conforms to all of the laws of writing a sefer Torah.
Taz, Orach Chaim 284:2, comments that the issue raised by Levush is already discussed in the Gemara. The Gemara, Gittin 60a, quotes Rabbah and Rav Yosef that one may not use a sefer aftarta (for the haftorah reading) on Shabbat. A sefer aftarta is a collection of all of the haftorah texts in one book (see Tosafot Rid, ad loc). The reason why one may not use a sefer aftarta is because one is not allowed to write Torah Shebichtav (the written scriptures) unless it is written following all of the laws of writing a sefer Torah. The Gemara then states that since nowadays, it is impossible to demand that all written scriptures be written like a sefer Torah, it is permitted to use a sefer aftarta.
Taz states that the leniency that allows one to use a sefer aftarta negates any requirement that one must use a text that conforms to all of the laws of writing a sefer Torah. The requirement to use parchment only applies when an entire book of Tanach is written. Therefore, the leniency to use a sefer aftarta implies a leniency to use paper instead of parchment.
The Use of the Printing Press
Taz notes that one can argue that the sefer aftarta has an advantage over the printed haftorah text. The sefer aftarta is written by hand, whereas the printed haftorah text is printed by machine. While the leniency to read from a sefer aftarta implies that there is no requirement that the haftorah be read from a text that has kedushat kitvei hakodesh (sanctity of one of the books of Tanach), there is a requirement that the text have some minimal level of sanctity. In order to achieve this minimal level of sanctity, the text must be written in a halachically valid form of writing.
With the invention of the printing press, numerous responsa were written discussing whether the printing press can produce a halachically valid form of writing. Teshuvot HaRama MiPanu no. 93, writes that the printing press can produce a halachically valid form of writing. R. Yair Bachrach, Teshuvot Chavot Yair, no. 16, argues that a printed item does not even have a minimal level of sanctity. Despite the potential distinction between hand written material and machine printed material, Taz follows the opinion of Rama MiPanu, and therefore allows reading the haftorah from a text printed by a printing press.
Magen Avraham, 284:1, notes that one does not require the leniency of sefer aftarta to allow the use of paper instead of parchment. He quotes the opinion of Tosafot, Shabbat 115b, s.v. Megillah, that the requirement to use parchment and proper ink only applies to a sefer Torah and not to the other books of Tanach. Therefore, the only leniency that the sefer aftarta necessitates is the allowance of a non-complete book of Tanach. In the times of the Gemara, it was too difficult to demand that every congregation own a complete set of nevi'im. Therefore, the rabbis allowed the use of the sefer aftarta. Magen Avraham contends that with the invention of the printing press this leniency is no longer applicable. The cost of a complete set of printed nevi'im is affordable, and it must be used for the haftorah reading.
Practical Differences Between Taz and Magen Avraham
According to Taz, the allowance to use printed materials is based on the Gemara's leniency to use a sefer aftarta. According to Magen Avraham, there is no leniency applied, and one may read from a text printed from a printing press. R. Moshe Sofer, Teshuvot Chatam Sofer, Orach Chaim no. 68, notes that if one assumes that reading from printed materials is based on the leniency of sefer aftarta, the recitation of the haftorah is considered as if it is recited ba'al peh (by heart). Tosafot, Temurah 14b, s.v. Devarim write that when reciting text from Tanach by heart, one cannot fulfill another person's obligation. Chatam Sofer suggests that since reading the haftorah from printed material is considered like recitation by heart, every person must read the haftorah along with the ba'al koreh. One cannot fulfill the obligation of haftorah by listening to the ba'al koreh. According to Magen Avraham, if one reads from a complete book of Tanach, there is no need to rely on the leniency to recite the haftorah by heart, and therefore, one can fulfill his obligation by listening to the ba'al koreh.
Another difference between the opinions of Magen Avraham and Taz lies in the requirement to use a complete book of Tanach. According to Magen Avraham, a congregation that can afford a complete set of Tanach must use it for the haftorah. According to Taz, nothing is gained by using a complete book written on paper.
Mishna Berurah seems to adopt the position of Magen Avraham. He rules (284:1) in accordance with Magen Avraham, that one must read from a complete book of Tanach, unless it is not available. He also rules (284:11) that if the haftorah is being read from a chumash, all of the congregants should read along with the ba'al koreh. If the haftorah is being read from a navi, the congregants should not read along with the ba'al koreh. The distinction between chumash and navi seems to be a distinction between a collection of haftarot and a complete book of Tanach. If the haftorah is read from a chumash, according to Chatam Sofer, every person must read the haftorah along with the ba'al koreh. If the haftorah is read from a complete book, it is not necessary for each person to read along with the ba'al koreh. [Alternatively, it is possible that Mishna Berurah does not totally accept the position of Magen Avraham. If so, when Mishna Berurah refers to "navi," he refers to a complete navi that is written in accordance with all of the laws of sefer Torah.]
Chazon Ish, Orach Chaim 60:11, and R. Yosef D. Soloveitchik (in Nefesh HaRav pg.161) present a major limitation to Magen Avraham's opinion. They suggest that printed material cannot be considered a complete book unless the left side of one page is connected to the right side of the next page. A book that has writing on both sides of the page, and is bound together by a binding is not considered a complete book. [According to this opinion, if one wants to fulfill the position of Magen Avraham, one can print the books of nevi'im on banner paper.]
Mishna Berurah, Sha'ar Hatziun 284:4, notes that since (at least according to Taz) the leniency to use printed materials is based on the inability of congregations to purchase properly written sifrei navi, congregations that can afford it should certainly purchase a set. R. Ovadia Yosef, Yechave Da'at 5:26, quotes Eliah Rabbah 284:3, who is of the opinion that using a sefer aftarta that is written in accordance with all of the laws of sefer Torah, is certainly better than using a printed text. R. Yosef therefore rules that if a congregation cannot afford a set of sifrei navi, they should purchase a sefer aftarta that is written on parchment. Mishna Berurah 284:1, in omitting the suggestion of Eliah Rabbah, implies that he prefers a complete book printed on paper over a sefer aftarta written on parchment.