Rule 10b-5 proscribes untrue statements of a material fact or omissions to state a material fact necessary in order to make the statements made, in the light of the circumstances under which they were made, not misleading.  This decision holds that “pure omissions” do not violate the regulation.  A pure omission occurs when a speaker says nothing, in circumstances that do not give any special significance to that silence.  Half-truths, on the other hand, are “representations that state the truth only so far as it goes, while omitting critical qualifying information.  Rule 10b-5 proscribes half-truths, but not pure omissions.