Chapter 29
Laws Derived from Isaiah: Running, Walking, Commerce, Measuring, Reading, Speaking
BUYING AND SELLING ON BHABBATH AND YOM TOV
18.a. As a result, one may go to one’s usual shopkeeper and take from him whatever* one needs for Shabbath or Yom Tov.
18.b. However (subject to the fuller explanation given in the succeeding paragraphs), one must not
1) quantify the amount one requires, by cost, weight
or measure, or
2) add it to previous purchases and specify the cumulative amount, by cost, weight, measure or number.
19.a. One should not ask a shopkeeper for a quantity of food by money’s worth, for instance fruit costing a total of so-and-so much, if one’s intention in mentioning the price is to state the limit of what one wants to spend, so as to ascertain how much the shopkeeper is willing to sell for this amount.
19.b. It is as well to avoid referring to cost even when the items have a fixed price and one’s intention is, by stating the total cost, to indicate to the shopkeeper the quantity one requires.
19.c. One may indicate the desired commodity even if one has to mention money for this purpose, as where there are two kinds of apples and one wants those costing so- and-so much.
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*See, however, paragraph 26 below.

