In discussing the timing of a motion for summary judgment, lawyers will often refer to "the one motion rule." There is no such rule as to summary judgment. "The one motion rule" is a statutory rule that applies only to motions to dismiss on the pleadings.
Under Civil Practice Laws and Rules ("CPLR'), section 3211(a) a party may move for judgment dismissing one or more causes of action asserted against him on a number of grounds such as that a defense is founded upon documentary evidence, or the court has not jurisdiction of the subject matter of the cause of action; or the party asserting the cause of action has not legal capacity to sue...", etc. As to the "Number, time and waiver of objections; motion to plead over....," CPLR 3211 (e) provides: "At any time before service of the responsive pleading is required, a party may move on one or more of the grounds set forth in subdivision (a), and no more than one such motion shall be permitted."
The "one motion rule" for motions to dismiss is based on the principle that, if the defendant is planning on moving to dismiss, since no discovery is necessary, the motion should contain all of the grounds on which the party intends to move. On the other hand, a motion for summary judgment comes after discovery. Whether and when there is enough support to make a summary judgment motion is a judgment calls. Consequently, courts want parties to put some thought into when it is appropriate to make the motion. Judges do not want to entertain a premature motion and they certainly don't want to consider a second motion for summary judgment necessitated by a party's failure to get all the evidence needed when the first motion was made. For that reason, while there is no absolute bar to more than one summary judgment, a second one will not be looked upon favorable unless there is an explanation for why it all could not be done in one motion.
As the one scholar observed:
It is rare that more than one summary judgment motion be made in a case, but there is no stated restriction in CPLR 3212. "Multiple summary judgment motions in the same action [are] discouraged in the absence of a showing of newly discovered evidence or other sufficient cause". One situation in which the courts allow a second motion for summary judgment is where "a new, as yet untested defense is permitted to be added by amendment"
Siegel, N.Y. Prac. § 279 (5th ed.).
This principle is illustrated in numerous cases.
"Generally, successive motions for summary judgment should not be entertained, absent a showing of newly discovered evidence or other sufficient cause (see Vinar v. Litman, 110 A.D.3d 867, 868, 972 N.Y.S.2d 704; Coccia v. Liotti, 101 A.D.3d 664, 666, 956 N.Y.S.2d 63; Sutter v. Wakefern Food Corp., 69 A.D.3d 844, 845, 892 N.Y.S.2d 764). Here, there was no showing of newly discovered evidence or other sufficient cause to warrant entertaining that branch of the motion"
Tingling v. C.I.N.H.R., Inc., 120 A.D.3d 570, 570, 992 N.Y.S.2d 43, 44 (2014)
"While we agree that successive motions for summary judgment are not to be encouraged (Levitz v. Robbins Music Corporation, 17 A.D.2d 801, 232 N.Y.S.2d 769), certainly a second motion for summary judgment should be entertained if, after a first motion for summary judgment, a new, as yet untested defense is permitted to be added by amendment."
Armstrong v. Peat, Marwick, Mitchell & Co., 150 A.D.2d 189, 191, 540 N.Y.S.2d 799, 801 (1989)
In conclusion, the "one motion rule" is a hard and fast rule on motions to dismiss. But there is no such rule for summary judgment. Nevertheless, the bottom line is - don't pull the trigger on a summary judgment motion if you are uncertain that you have all the evidence or all the grounds. If you fire too soon, the court will not be happy to see you on a second motion supported by evidence or theories that should have been in the first motion