840
Opinion of the Court
ard that is consistent with the Cruel and Unusual Punishments Clause as interpreted in our cases, and we adopt it as the test for "deliberate indifference" under the Eighth Amendment.
2
Our decision that Eighth Amendment liability requires consciousness of a risk is thus based on the Constitution and our cases, not merely on a parsing of the phrase "deliberate indifference." And we do not reject petitioner's arguments for a thoroughly objective approach to deliberate indifference without recognizing that on the crucial point (whether a prison official must know of a risk, or whether it suffices that he should know) the term does not speak with certainty. Use of "deliberate," for example, arguably requires nothing more than an act (or omission) of indifference to a serious risk that is voluntary, not accidental. Cf. Estelle, 429 U. S., at 105 (distinguishing "deliberate indifference" from "accident" or "inadverten[ce]"). And even if "deliberate" is better read as implying knowledge of a risk, the concept of constructive knowledge is familiar enough that the term "deliberate indifference" would not, of its own force, preclude a scheme that conclusively presumed awareness from a risk's obviousness.
Because "deliberate indifference" is a judicial gloss, appearing neither in the Constitution nor in a statute, we could not accept petitioner's argument that the test for "deliberate indifference" described in Canton v. Harris, 489 U. S. 378 (1989), must necessarily govern here. In Canton, interpreting Rev. Stat. § 1979, 42 U. S. C. § 1983, we held that a municipality can be liable for failure to train its employees when the municipality's failure shows "a deliberate indifference to the rights of its inhabitants." 489 U. S., at 389 (internal quotation marks omitted). In speaking to the meaning of the term, we said that "it may happen that in light of the duties assigned to specific officers or employees the need for
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