Mr. Justice Van Orsdel

delivered the opinion of-the Court:

In stating the case presented by the pleadings, we have ignored the question of privileged communication, for the reason that the judgment can be sustained upon the plea of former adjudication. The conclusiveness of the judgment in a prior suit between the same parties must be ascertained from the record in that case, or by extrinsic evidence that the question involved in the present action was raised and determined in the former case. It is not denied that the matter here complained of was involved in the former suit. In fact, its existence there forms the basis of this action. But it is contended that the present suit is a different cause of action from the former one, and that the alleged conspiracy was not complete, and the overt act here complained of had not been committed, until after the former suit was instituted. The mere fact that a different cause of action is involved, so long as the same parties are concerned, will not prevent the plea of estoppel. The rule was announced in Southern P. R. Co. v. United States, 168 U. S. 1, 42 L. ed. 355, 18 Sup. Ct. Rep. 18, as follows: “The general principle announced in numerous cases is that a right, question, or fact distinctly put in issue and directly determined by. a court of competent jurisdiction, as a ground of recovery, canhiot be disputed in a subsequent suit between the same parties or their privies; and even if the second suit.is for a different cause of action, the right, question, or fact, once so determined, must, as between the same parties or their privies, be taken as *41conclusively established, so long as the judgment in the first suit remains unmodified.”

Neither is it important that the alleged libel was not in existence at the time of the filing of the former suit. If it was involved in the mandamus proceeding, and its determination was an essential element of the judgment, plaintiff cannot make it the basis of an action for libel. We understand the rule of res judicata to be that a judgment or decree rendered by a court of competent jurisdiction is conclusive not only upon all matters directly involved in the issue under consideration, but upon all matters properly put in litigation, or that could have been adjudicated therein. “The plea of res judicata applies, except in special cases, not only to the points upon which the court was required by the parties to form an opinion and pronounce a judgment, but to every point which properly belonged to the subject of litigation, and which the parties, exercising reasonable diligence, might have brought forward at the time.” Beloit v. Morgan, 7 Wall. 619, 19 L. ed. 205. The alleged libel, forming the basis of the present suit, not only could properly have been determined in the mandamus proceeding, but clearly was determined, and formed a material issue in arriving at the judgment therein.

While the opinion of the trial court is not part of the record in that case, we may look to it to ascertain what was in the mind of the court when the judgment was rendered. In considering the portion of the answer here involved, which constituted the chief defense of the defendants in that action, the learned justice said: “In the absence of any prohibition in the statute, the power is inherent in the board to dismiss teachers for want of suitable qualifications as such. * * * The return or answer to the rule in this case must be considered as meaning, and is admitted by the demurrer to mean, that upon examination (that, is, upon observation and inquiry into the qualifications and competency of this relator in her capacity as teacher) they found her to be ‘deficient in the necessary academic and pedagogic equipmjnt of i competent teacher and that in the exercise of their duty as well as their authority, *42as they regarded it, they dismissed her for the good of the service. * * * The general power of the board to' dismiss a teacher in a proper case is expressly conferred, subject to one condition,^ — that such dismissal shall be ‘upon written recommendation of the superintendent of schools.’ * * * That Congress never intended to tie the hands of the board of education so that it could not dismiss a teacher who was found to be lacking in the necessary qualifications of a competent teacher is not only evidenced by the act itself, but, in the very nature of things, it must be so.”

This court, in affirming the judgment (United States ex rel. Nalle v. Hoover, 31 App. D. C. 311), said: “The answer of respondents sets forth that relator was dismissed because she was lacking in the academic and pedagogic equipment of a competent teacher. * * * If the board had power to dismiss relator upon the recommendation of the superintendent of schools, without granting her such a hearing as is provided for in sec. 10 of the act, we will not stop to inquire into the method employed by the board in arriving at its decision.”

It will be observed that the judgment of the court below and the opinion of this court rest upon the fact that the board had found the plaintiff deficient in the necessary qualifications of a teacher, and that the examination mentioned in the statute required no formal hearing, but might consist of any information the- members of the board might gather, individually or collectively, that would, in their judgment, justify her dismissal. It will also be observed that the allegations of the answer involved formed the very basis of the judgment dismissing the mandamus proceeding. It was the duty of the defendants (the board, in that case) to state in their answer wliy they had dismissed the plaintiff; and it was upon this allegation and the proof adduced at the trial that the writ was denied.

We are therefore of the opinion cl,.at the main question of fact involved in the present case is shown by the record not only to have been put in issue in the former case, but to have been there decided adversely to the plaintiff. The judgment is affirmed, with costs, and it is so ordered* Affirmed.