The cancellation of the Rosh Chodesh reading in favor of the weekly portion, on the basis of the rule of tadir
Question
Shalom,It is known that when something is frequent (תדיר) and something is not frequent (שאינו תדיר), the frequent takes precedence. Why then, when Rosh Chodesh falls on Monday, do we read the Torah the portion of Rosh Chodesh and not the weekly portion?
Answer
Shalom uVracha,
This can be explained in two ways:
A. The reading of the weekly portion is not actually more frequent, since it is read only once a year [or four times, including the readings on Shabbos Mincha, Monday, and Thursday], whereas the Rosh Chodesh reading is read every month, sometimes even twice in the same month.
B. The enactment of Moshe Rabbeinu to read the Torah on Monday, Thursday, and Shabbos does not override the enactment to read a portion that is connected to a specific time, for when that time arrives, its reading takes precedence.
Comments

- Top halachic Q&A
- Practical festival halachot