However, other passages exist dismissing either in whole or in part the impact of dreams, such as “dreams speak falsehood” (Berakhot 55b), and one is only shown in his dream the thoughts of his heart [during the day], and “the contents of dreams do not add or subtract" (Sanhedrin 30a; Gittin 52a; Horiot 13b; Yerushalmi, Ma’aser Sheni 4:6). The story is told (Tosefta, Ma’aser Sheni, ch. 5) of a man who was worried about missing ma’aser sheni money, and learned of its location in a dream; when the information was confirmed and the money was found, he was permitted by the rabbis to use it for personal purposes, because of the unreliability of dreams.
Several theories exist to resolve these attitudes:
The Resp. Tashbetz (II, 125) posits that the issue is whether the subject of the dream is the dreamer himself or someone else. One should take seriously the implications of his own dreams; someone else’s dreams, however, can be dismissed. In a lengthy responsum, he proceeds to also suggest that internal spiritual, psychological, and physiological factors can impact the accuracy of dreams. Further, he notes that the attitude may differ depending on what area of halakhah is affected. The case involving ma’aser sheni would require removing money from the one in possession (muchzak), which demands a very high standard of proof. The case of excommunication, however, results in an indeterminate status (safek), and thus, out of stringency, must be dealt with.
The Resp. Rav Poalim (II, 32), in resolution of the ma’aser sheni/excommunication passages, builds on the Talmudic notion that dreams are partially true and partially false (see also his citation of Resp. Chatam Sofer, Y.D, 222, on this point). Thus, in the ma’aser sheni case, the location was confirmed, and is thus the true part; the ma’aser sheni status must consequently be the false part. In the excommunication case, since part of the dream is assumed to be true, the possibility that it is the existence of the excommunication must be accounted for, at least out of stringency.
(An innovative approach, combining elements similar to the last two, is advanced by R. Y. Ya’akov Neuman, in the journal HaDarom, vol. XXVIII, pp. 65-68. See also that article for a listing of rishonim who endorse or reject the significance of dreams.)
The Klausenberger Rebbe (Resp. Divrei Yatziv, Y.D. 121) assumes that the controlling factor in the accuracy of a dream is the righteousness of the dreamer; a particularly holy individual has dreams of a different quality than an average person. To this point, he quotes the Resp. M’kom Shmuel (#11) objecting to the Shach’s (C.M. 336:2) questioning of a dream by someone of the stature of the Maharam Rotenberg.
The Resp. Shivat Tziyon (52) suggests that as dreams are considered prophetic, they are to be taken seriously, but only as regards the future; dreams that refer to the past may be dismissed, as they have no ability to establish existent reality.
The Arukh HaShulchan (288:7) asserts that heeding the impact of dreams is a decision left up to the individual; it is for that reason that one who undertakes a ta’anit chalom on Shabbat must later atone, as it is considered a matter of choice. The Iyyunim B’Halakhah (III, 18) takes issue with this, and notes the comment of the Ritva (Ta’anit 12b), that although the contents of dreams can often be dismissed, those that appear to carry a direct personal message to the dreamer, such as a call to repentance, should not be ignored.