The Wisconsin Department of Revenue appeals from a judgment reversing the Tax Appeals Commission's decision upholding the department's assessment of additional franchise tax against Pabst Brewing Company. The issue is whether Pabst's sales of beer to out-of-state wholesalers who pick up the beer at its Milwaukee plant for out-of-state distribution are sales "in this state" under sec. 71.07(2)(c)2, Stats. We conclude that because the location of the purchasing wholesaler rather than the pickup controls whether the sales are in this state, the beer pickups are not sales "in this state.” We therefore affirm the judgment.
*294The relevant facts are undisputed. Pabst operates a brewery in Milwaukee. Because it sells beer to instate and out-of-state wholesalers, Pabst apportions its net income for Wisconsin tax purposes on the basis of property, payroll and sales factors established in sec. 71.07(2), Stats. The sales factor is a fraction. The numerator is the taxpayer's total sales in Wisconsin, and the denominator is its total sales everywhere. Section 71.07(2)(c)l. Sales of tangible personal property are "in this state" and included in the numerator if "the property is delivered or shipped to a purchaser, other than the United States government, within this state regardless of the f.o.b. point or other conditions of the sale. . . ." Section 71.07(2)(c)2. When computing its sales factor between 1973 and 1977, Pabst excluded from the numerator all beer sold to out-of-state wholesalers. The department subsequently assessed Pabst an additional $707,729.71 in taxes for these years. The assessment resulted from the department's treating beer pickups in Wisconsin by out-of-state wholesalers as Wisconsin sales and adding those sales to the numerator. Pabst challenged the resulting assessment before the Tax Appeals Commission and circuit court. The commission upheld the department's determination and the circuit court reversed.
The meaning of sec. 71.07(2)(c)2, Stats., is the issue before us. The meaning of a statute is a question of law which we review without deference to the trial court's decision. Revenue Dept. v. Milwaukee Brewers, 111 Wis. 2d 571, 577, 331 N.W.2d 383, 386 (1983). The aim of statutory construction is to discern the legislature's intent. State v. Denter, 121 Wis. 2d 118, 122, 357 N.W.2d 555, 557 (1984). Rules of construction are used only to *295determine the meaning of an ambiguous statute. State v. Tollefson, 85 Wis. 2d 162, 167, 270 N.W.2d 201, 203 (1978). If a statute is ambiguous, to arrive at its reasonable meaning, we look to its statutory context, subject matter, scope, history and the object to be accomplished. St. John Vianney Sch. v. Janesville Ed. Bd., 114 Wis. 2d 140, 151, 336 N.W.2d 387, 391 (Ct.App. 1983); In Interest of I.V., 109 Wis. 2d 407, 409-10, 326 N.W.2d 127, 129 (Ct.App. 1982).
A statute is ambiguous if reasonable persons could disagree as to its meaning. Kollasch v. Adamany, 104 Wis. 2d 552, 561, 313 N.W.2d 47, 51-52 (1981). Whether a statute is ambiguous is a question of law. St. John Vianney, 114 Wis. 2d at 150, 336 N.W.2d at 391.
We conclude sec. 71.07(2)(c)2, Stats., ambiguously treats out-of-state purchasers. Two reasonable readings are possible. The phrase "within this state" may be read to modify "delivered or shipped." That reading makes the purchaser's physical possession of the product in Wisconsin the condition for a Wisconsin sale. The department and commission read the statute that way to conclude that Pabst's sales to out-of-state wholesalers who pick up the product in Milwaukee are sales "in this state." Alternatively, the phrase "within this state" may be read to modify "purchaser" rather than "delivered or shipped." If that is the reading, the purchaser's business location controls. Pabst argued and the circuit court accepted this position.
The parties advance alternative rules of construction to resolve the ambiguity. Pabst argues that an ambiguity in a tax statute must be resolved in favor of the taxpayer. Dept. of Revenue v. Milwaukee Refining *296Corp., 80 Wis. 2d 44, 48-49, 257 N.W.2d 855, 858 (1977). The department argues that deference is accorded to its reading, since it administers the state's tax laws. Revenue Dept. v. Lake Wisconsin Country Club, 123 Wis. 2d 239, 242-43, 365 N.W.2d 916, 918 (Ct.App. 1985). Each approach is tempered, however, by the principle that a rule of construction cannot be used to defeat the legislature's intent. American Motors Corp. v. ILHR Dept., 101 Wis. 2d 337, 350-51, 356, 305 N.W.2d 62, 68, 71 (1981); Milwaukee Refining, 80 Wis. 2d at 49, 257 N.W.2d at 858.
We conclude that the legislature intends "within this state" to modify "purchaser." Section 71.07(2)(c)2, Stats., provides that whether a sale occurs in this state is unaffected by "f.o.b. point or other conditions of the sale." The legislature's intent regarding the effect of those two factors is beyond dispute. Yet the department's approach makes a condition of the sale, the method of delivery, the central factor when determining Wisconsin sales, notwithstanding the contrary legislative intent expressed in sec. 71.07(2)(c)2. We therefore conclude that the location of the purchaser controls. That out-of-state wholesalers pick up Pabst's beer in Wisconsin rather than having it delivered is therefore immaterial. The department incorrectly relied on this distinction to impose additional franchise tax on Pabst.
By the Court. — Judgment affirmed.