Thomas was responding to a question about the Court’s review of the McCain-Feingold Campaign Finance Law.  His quote echoes former Justice Felix Frankfurter (who happened to have been the president of the ACLU before his court days).  Here is Frankfurter’s quote:

“The ultimate touchstone of constitutionality is the Constitution, and not what we have said about it.”  — Felix Frankfurter, Graves v. New York, 306 US 466 (1939)

Here is an audio clip of Justice Thomas’ remarks:

Here are a few more quotes to chew on:

“[I]n the lapse of [time], changes have taken place which in particular passages … obscure the sense of the original … [and] present wrong signification or false ideas. Whenever words are understood in a sense different from that which they had when introduced …. mistakes may be very injurious.” Noah Webster in Preface of the Webster Bible

“Though written constitutions may be violated in moments of passion or delusion, they furnish a text to which those who are watchful may again rally.”  — Thomas Jefferson

“On every question of construction (of the Constitution) let us carry ourselves back to the time when the Constitution was adopted, recollect the spirit manifested in the debates, and instead of trying what meaning may be squeezed out of the text, or invented against it, conform to the probable one in which it was passed.”  — Thomas Jefferson, letter to William Johnson, June 12, 1823, The Complete Jefferson, p322.

“The first and fundamental rule in the interpretation of all instruments is, to construe them according to the sense of the terms, and the intentions of the parties.” Justice Joseph Story, III Commentaries on the Constitution of the United States §400 (1883) at p383