Catalina M. de Leon commenced this action in the Court of First Instance of  Quezon  City to  make effective  the purchase she made of one-half of a parcel of  land from spouses Rosario B. de Leon and Francisco de Leon for the Bum of P1,000.  She avers that said spouses acquired the land from Perfecto Roque  and Aurelio Bautista by virtue of a document executed on July 11, 1949 which was ratified before a notary public; that Perfecta Rogue  and Aurelio Bautista in turn acquired the land from the People Homesite Corporation  on installment  basis; that plaintiff  demanded from the spouses Rosario B. de Leon and Francisco de Leon the formal execution of the transfer made in  her favor as well as the registration of the transfer in  the office of the People's Home Site Corporation but said spouses refused to agree to her  demand; that Perfecta Roque and, Aurelio Bautista, instead  of recording the transfer they made  of the land to spouses' Rosario B. de Leon and Francisco  de Leon  with the "People's Homesite Corporation, fraudulently conveyed it to one Petronilo Castafieda; that the  People's  Homesite  Corporation  refused  to  recognize her right over  one-half of the land notwithstanding her demand, and to make effective her right' she instituted  the present action making as party defendants all the parties in interest as above mentioned.  Plaintiff also alleges that the defendants  conspired to defeat and render ineffective her right over the land and, as  a consequence, she prays for damages  in the amount of P18.000.

Defendants Perfecta Roque and  Aurelio  Bautista filed a motion to  dismiss on the grounds  that  the  action  is already barred  by a prior  judgment  and the complaint states no cause of action.   Main basis of the  motion is a decision rendered by the Court of First Instance of Quezon City on December 22, 1950, wherein the transfer of the land  made  by  Perfecta Roque and Aurelio  Bautista to spouses Rosario B.  de  Leon and  Francisco de Leon was declared  rescinded and  without  effect and,  hence,  said spouses could not have transferred any right to the plaintiff.

Judge Magno  S.  Gatmaitan, then  presiding  over  the court,  denied  the motion stating that the  grounds alleged do not appear to be indubitable it appearing that plaintiff was not a party to the case invoked and she alleged conspiracy on the part of the defendants.  But, on a motion for reconsideration, Judge Hermogenes  Caluag,  who took over the court, reversed the former ruling and  dismissed the case without pronouncement as to costs.  This is  the order which is now the subject of the present appeal.

In  its order dismissing the case for lack of sufficient cause of action, the trial court took into account the decision rendered in Civil Case No. 9366 wherein the transfer of the land made by Perfecta Roque  and Aurelio Bautista in favor of  spouses Rosario B.  de Leon and. Francisco de Leon was rescinded and it concluded that as a result of such  rescission,  plaintiff  could not  have  acquired  any right from said spouses which may be the basis, of relief in the present action.   The reasoning of the trial court is that,  Catalina de Leon, plaintiff herein,  being  merely a successor in  interest of spouses  De Leon, the  judgment rendered in said case against them is binding upon her.

The finding of the trial court that the decision rendered in Civil Case No. 9366 has the effect of res judicata which bars plaintiff from pressing her claim in the present action is based on a wrong premise for it ignores the fact that plaintiff had  acquired her interest in the land prior to the institution of said  case, and hence she  could not be considered as successor in  interest  of spouses De Leon.  This is the postulate of  section  44 (6), Rule  39, which provide that "In other cases the judgment so ordered is,  in respect to the matter directly adjudged, conclusive between the parties and their successors in interest by title, subsequent to commencement of the action or special proceeding, litigating for the  same thing and under the same title and in the same capacity."  Note that to be a successor in  interest a  purchaser must,,acquire subsequent to  the  commencement of the action, and not before as in the present case.   If  an action is  filed against  the vendor after he had parted with his title in favor of a third person, the latter is, not bound  by  any judgment which may be rendered  against the former.   In  such  a case the principle of res judicata does not apply  (Moran,  Comments on the Rules of Court, Vol. I, 1952  ed., 870).  The trial court therefore  erred in applying this  principle to the present case.

Another factor that the trial court has overlooked is the fact that the complaint alleges collusion and conspiracy on the part of the defendants to defeat and render ineffective the right acquired by the plaintiff which claim necessarily puts in issue the alleged rescission of the transfer made by Perfecta Rogue and  Aurelio Bautista  to  spouses Rosario B. de Leon and Francisco de Leon.  With the presentation of the motion to dismiss defendants are  deemed to have admitted the aforesaid claim of conspiracy and this creates a situation which negatives any  favorable action  on the motion to dismiss.   The proper course the trial court would have taken is to defer consideration of the motion until trial pursuant  to section S, Rule 8, considering that the ground alleged does not appear to be indubitable, as was done by Judge Gatmaitan who  originally acted in the motion to  dismiss.

Wherefore, the order appealed  from  is set aside.  The case is remanded to the lower court for further proceedings, with  costs against appellees.

Parás, C. J., Padilla, Montemayor, Reyes, A., Jugo, Labrador,  Concepcion, Reyes, J. B. L. and Endencia, JJ., concur.