opinion: Mr. Justice Frankfurter
  delivered the opinion of the Court.
  The respondent Rumely was Secretary of an organization known as the Committee for Constitutional Government, which, among other things, engaged in the sale of books of a particular political tendentiousness. He refused to disclose to the House Select Committee on Lobbying Activities the names of those who made bulk purchases of these books for further distribution, and was convicted under R. S. § 102, as amended, 52 Stat. 942, 2 U. S. C. § 192, which provides penalties for refusal to give testimony or to produce relevant papers “upon any matter” under congressional inquiry. The Court of Appeals reversed, one judge dissenting. It held that the committee before which Rumely refused to furnish this information had no authority to compel its production. 90 U. S. App. D. C. 382, 197 F. 2d 166. Since the Court of Appeals thus took a view of the committee’s authority contrary to that adopted by the House in citing Rumely for contempt, we granted certiorari. 344 U. S. 812. This issue — whether the committee was authorized to exact the information which the witness withheld — must first be settled before we may consider whether Congress had the power to confer upon the committee the authority which it claimed.
  Although we are here dealing with a resolution of the House of Representatives, the problem is much the same as that which confronts the Court when called upon to construe a statute that carries the seeds of constitutional controversy. The potential constitutional questions have far-reaching import. We are asked to recognize the penetrating and pervasive scope of the investigative power of Congress. The reach that may be claimed for that power is indicated by Woodrow Wilson’s characterization of it:
  “It is the proper duty of a representative body to look diligently into every affair of government and to talk much about what it sees. It is meant to be the eyes and the voice, and to embody the wisdom and will of its constituents. Unless Congress have and use every means of acquainting itself with the acts and the disposition of the administrative agents of the government, the country must be helpless to learn how it is being served’ and unless Congress both scrutinize these things and sift them by every form of discussion, the country must remain in embarrassing, crippling ignorance of the very affairs which it is most important that it should understand and direct. The informing function of Congress should be preferred even to its legislative function.” Wilson, Congressional Government, 303.
  Although the indispensable “informing function of Congress” is not to be minimized, determination of the “rights” which this function implies illustrates the common juristic situation thus defined for the Court by Mr. Justice Holmes: “All rights tend to declare themselves absolute to their logical extreme. Yet all in fact are limited by the neighborhood of principles of policy which are other than those on which the particular right is founded, and which become strong enough to hold their own when a certain point is reached.” Hudson Water Co. v. McCarter, 209 U. S. 349, 355. President Wilson did not write in light of the history of events since he wrote; more particularly he did not write of the investigative power of Congress in the context of the First Amendment. And so, we would have to be that “blind” Court, against which Mr. Chief Justice Taft admonished in a famous passage, Child Labor Tax Case, 259 U. S. 20, 37, that does not see what “[a] 11 others can see and understand” not to know that there is wide concern, both in and out of Congress, over some aspects of the exercise of the congressional power of investigation.
  Accommodation of these contending principles — the one underlying the power of Congress to investigate, the other at the basis of the limitation imposed by the First Amendment — is not called for until after we have construed the scope of the authority which the House of Representatives gave to the Select Committee on Lobbying Activities. The pertinent portion of the resolution of August 12, 1949, reads:
  “The committee is authorized and directed to conduct a study and investigation of (1) all lobbying activities intended to influence, encourage, promote, or retard legislation; and (2) all activities of agencies of the Federal Government intended to influence, encourage, promote, or retard legislation.” H. Res. 298, 81st Cong., 1st Sess.
  This is the controlling charter of the committee’s powers. Its right to exact testimony and to call for the production of documents must be found in this language. The resolution must speak for itself, since Congress put no gloss upon it at the time of its passage. Nor is any help to be had from the fact that the purpose of the Buchanan Committee, as the Select Committee was known, was to try to “find out how well [the Federal Regulation of Lobbying Act of 1946, 60 Stat. 839] worked.” 96 Cong. Rec. 13882. That statute had a section of definitions, but Congress did not define the terms “lobbying” or “lobbying activities” in that Act, for it did not use them. Accordingly, the phrase “lobbying activities” in the resolution must be given the meaning that may fairly be attributed to it, having special regard for the principle of constitutional adjudication which makes it decisive in the choice of fair alternatives that one construction may raise serious constitutional questions avoided by another. In a long series of decisions we have acted on this principle. In the words of Mr. Chief Justice Taft, “[i]t is our duty in the interpretation of federal statutes to reach a conclusion which will avoid serious doubt of their constitutionality.” Richmond Co. v. United States, 275 U. S. 331, 346. Again, what Congress has written, we said through Mr. Chief Justice (then Mr. Justice) Stone, “must be construed with an eye to possible constitutional limitations so as to avoid doubts as to its validity.” Lucas v. Alexander, 279 U. S. 573, 577. As phrased by Mr. Chief Justice Hughes, “if a serious doubt of constitutionality is raised, it is a cardinal principle that this Court will first ascertain whether a construction of the statute is fairly possible by which the question may be avoided.” Crowell v. Benson, 285 U. S. 22, 62, and cases cited.
  Patently, the Court’s duty to avoid a constitutional issue, if possible, applies not merely to legislation technically speaking but also to congressional action by way of resolution. See Federal Trade Comm’n v. American Tobacco Co., 264 U. S. 298. Indeed, this duty of not needlessly projecting delicate issues for judicial pronouncement is even more applicable to resolutions than to formal legislation. It can hardly be gainsaid that resolutions secure passage more casually and less responsibly, in the main, than do enactments requiring presidential approval.
  Surely it cannot be denied that giving the scope to the resolution for which the Government contends, that is, deriving from it the power to inquire into all efforts of private individuals to influence public opinion through books and periodicals, however remote the radiations of influence which they may exert upon the ultimate legislative process, raises doubts of constitutionality in view of the prohibition of the First Amendment. In light of the opinion of Prettyman, J., below and of some of the views expressed here, it would not be seemly to maintain that these doubts are fanciful or factitious. Indeed, adjudication here, if it were necessary, would affect not an evanescent policy of Congress, but its power to inform itself, which underlies its policy-making function. Whenever constitutional limits upon the investigative power of Congress have to be drawn by this Court, it ought only to be done after Congress has demonstrated its full awareness of what is at stake by unequivocally authorizing an inquiry of dubious limits. Experience admonishes us to tread warily in this domain. The loose language of Kilbourn v. Thompson, 103 U. S. 168, the weighty criticism to which it has been subjected, see, e. g., Fairman, Mr. Justice Miller and the Supreme Court, 332-334; Landis, Constitutional Limitations on the Congressional Power of Investigation, 40 Harv. L. Rev. 153, the inroads that •have been made upon that case by later cases, McGrain v. Daugherty, 273 U. S. 135, 170-171, and Sinclair v. United States, 279 U. S. 263, strongly counsel abstention from adjudication unless no choice is left.
  Choice is left. As a matter of English, the phrase “lobbying activities” readily lends itself to the construction placed upon it below, namely, “lobbying in its commonly accepted sense,” that is, “representations made directly to the Congress, its members, or its committees,” 90 U. S. App. D. C. 382, 391, 197 F. 2d 166, 175, and does not reach what was in Chairman Buchanan’s mind, attempts “to saturate the thinking of the community.” 96 Cong. Rec. 13883. If “lobbying” was to cover all activities of anyone intending to influence, encourage, promote or retard legislation, why did Congress differentiate between “lobbying activities” and other “activities . . . intended to influence” ? Had Congress wished to authorize so extensive an investigation of the influences that form public opinion, would it not have used language at least as explicit as it employed in the very resolution in question in authorizing investigation of government agencies? Certainly it does no violence to the phrase “lobbying activities" to give it a more restricted scope. To give such meaning is not barred by intellectual honesty. So to interpret is in the candid service of avoiding a serious constitutional doubt. “Words have been strained more than they need to be strained here in order to avoid that doubt.” (Mr. Justice Holmes in Blodgett v. Holden, 275 U. S. 142, 148, with the concurrence of Mr. Justice Brandéis, Mr. Justice Sanford and Mr. Justice Stone.) With a view to observing this principle of wisdom and duty, the Court very recently strained words more than they need be strained here. United States v. C. I. O., 335 U. S. 106. The considerations which prevailed in that case should prevail in this.
  Only a word need be said about the debate in Congress after the committee reported that Rumely had refused to produce the information which he had a right to refuse under the restricted meaning of the phrase “lobbying activities.” The view taken at that time by the committee and by the Congress that the committee was authorized to ask Rumely for the information he withheld is not legislative history defining the scope of a congressional measure. What was said in the debate on August 30, 1950, after the controversy had arisen regarding the scope of the resolution of August 12, 1949, had the usual infirmity of post litem motam, self-serving declarations. In any event, Rumely’s duty to answer must be judged as of the time of his refusal. The scope of the resolution defining that duty is therefore to be ascertained as of that time and cannot be enlarged by subsequent action of Congress.
  Grave constitutional questions are matters properly to be decided by this Court but only when they inescapably come before us for adjudication. Until then it is our duty to abstain from marking the boundaries of congressional power or delimiting the protection guaranteed by the First Amendment. Only by such self-restraint will we avoid the mischief which has followed occasional departures from the principles which we profess.
  The judgment below should be
  Affirmed.
  Mr. Justice Burton and Mr. Justice Minton took no part in the consideration or decision of this case.
  The ambiguity of the terms of the resolution — that is, whether questions asked to which answers were refused were within those terms — is reflected by the close division by which the committee’s view of its own authority prevailed. The vote was 183 to 175.
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