482
Opinion of the Court
tory command to examine the effect of the impairment on the major life activities "of such individual." And even if the statute is ambiguous, respondent claims, the guidelines' directive to ignore mitigating measures is not reasonable, and thus this Court should not defer to it.
We conclude that respondent is correct that the approach adopted by the agency guidelines—that persons are to be evaluated in their hypothetical uncorrected state—is an impermissible interpretation of the ADA. Looking at the Act as a whole, it is apparent that if a person is taking measures to correct for, or mitigate, a physical or mental impairment, the effects of those measures—both positive and negative— must be taken into account when judging whether that person is "substantially limited" in a major life activity and thus "disabled" under the Act. Justice Stevens relies on the legislative history of the ADA for the contrary proposition that individuals should be examined in their uncorrected state. See post, at 499-501 (dissenting opinion). Because we decide that, by its terms, the ADA cannot be read in this manner, we have no reason to consider the ADA's legislative history.
Three separate provisions of the ADA, read in concert, lead us to this conclusion. The Act defines a "disability" as "a physical or mental impairment that substantially limits one or more of the major life activities" of an individual. § 12102(2)(A) (emphasis added). Because the phrase "substantially limits" appears in the Act in the present indicative verb form, we think the language is properly read as requiring that a person be presently—not potentially or hypothetically—substantially limited in order to demonstrate a disability. A "disability" exists only where an impairment "substantially limits" a major life activity, not where it "might," "could," or "would" be substantially limiting if mitigating measures were not taken. A person whose physical or mental impairment is corrected by medication or other measures does not have an impairment that presently "sub-
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