The choice between a Rule 12(b)(6) motion and a Rule 56 motion isn’t always obvious, and picking the wrong vehicle can waste months and antagonize the court. These two motions test fundamentally different things, operate on different records, and carry different strategic consequences. Here’s how to think through the decision.
What Each Motion Actually Tests
A 12(b)(6) motion lives entirely within the four corners of the complaint (and documents incorporated by reference or subject to judicial notice). The question is whether the plaintiff has pleaded enough to state a plausible claim. The rule is blunt about it:
(b) How to Present Defenses. Every defense to a claim for relief in any pleading must be asserted in the responsive pleading if one is required. But a party may assert the following defenses by motion: … (6) failure to state a claim upon which relief can be granted
The governing standard comes from Bell Atlantic Corp. v. Twombly, 550 U.S. 544 (2007) and Ashcroft v. Iqbal, 556 U.S. 662 (2009). You know the drill: strip out conclusory allegations, accept the remaining factual allegations as true, and ask whether they plausibly give rise to relief. Courts don’t ask whether the plaintiff will win; they ask whether the claim is plausible on its face.
Summary judgment under Rule 56 is a different animal. It tests whether there’s a genuine factual dispute that needs to go to a jury:
(a) Motion for Summary Judgment or Partial Summary Judgment. A party may move for summary judgment, identifying each claim or defense, or the part of each claim or defense, on which summary judgment is sought. The court shall grant summary judgment if the movant shows that there is no genuine dispute as to any material fact and the movant is entitled to judgment as a matter of law. The court should state on the record the reasons for granting or denying the motion.
At this stage, you’re working with actual evidence: depositions, documents, declarations, interrogatory answers. The court doesn’t assume the plaintiff’s version is true in the same generous way. It looks at what the record actually shows.
When to Use Which
File a 12(b)(6) when the problem is with the pleading itself. Classic situations: the complaint lacks facts sufficient to establish an essential element, the claim is legally foreclosed regardless of what the facts might show, the statute of limitations bars the claim on the face of the complaint, or the plaintiff has pleaded themselves out of court by including facts that defeat their own claim.
Go to summary judgment when you need the actual record to win. You’ve taken discovery, and the plaintiff either has no evidence on an essential element or the undisputed facts establish your defense as a matter of law. This is the right tool when a 12(b)(6) would fail because the complaint is technically adequate but the case has no evidentiary foundation.
The timing difference matters too. Rule 56(b) allows a motion “at any time until 30 days after the close of all discovery,” and some courts allow early summary judgment motions before discovery closes. A 12(b)(6) motion is typically filed before or in lieu of an answer, though a failure-to-state-a-claim defense can also be raised via a Rule 12(c) motion for judgment on the pleadings after the pleadings close.
The Conversion Trap
This is where practitioners get burned. Rule 12(d) is a landmine if you’re not paying attention:
(d) Result of Presenting Matters Outside the Pleadings. If, on a motion under Rule 12(b)(6) or 12(c), matters outside the pleadings are presented to and not excluded by the court, the motion must be treated as one for summary judgment under Rule 56. All parties must be given a reasonable opportunity to present all the material that is pertinent to the motion.
Attach the wrong exhibit to your 12(b)(6) and you may have just converted your motion to dismiss into a summary judgment motion, potentially before discovery is complete. Courts have discretion to exclude the outside material and keep it as a 12(b)(6), but many don’t. If your motion gets converted and the plaintiff then argues they need discovery to oppose it under Rule 56(d), you’ve handed them a delay and potentially torpedoed your own motion.
The common mistake: defense counsel attaches a contract or corporate record to their 12(b)(6) thinking it’s incorporated by reference in the complaint, when it actually isn’t. The incorporation-by-reference doctrine is narrower than people think. If the complaint merely mentions the document, that’s usually not enough. The document typically needs to be central to the plaintiff’s claim and the authenticity must be undisputed.
Strategic Considerations
A 12(b)(6) win terminates the case before discovery, which is the gold standard for defendants in complex commercial litigation. Discovery in a large commercial case can run into the millions of dollars, so even a decent shot at a 12(b)(6) dismissal is worth evaluating carefully.
That said, don’t file a 12(b)(6) just to file one. A weak motion that gets denied accomplishes nothing except telegraphing your defenses, burning your one pre-answer motion opportunity under Rule 12(g)(2), and annoying the judge. If the complaint is technically adequate and the real weaknesses are evidentiary, save your ammunition for summary judgment.
For plaintiffs opposing a 12(b)(6), resist the urge to rely on your own factual submissions. Your job is to point to the well-pleaded factual allegations in the complaint and argue their sufficiency. If the complaint is genuinely thin, the better play may be to seek leave to amend rather than litigate a losing opposition. On the summary judgment side, if you legitimately need discovery to oppose the motion, file a Rule 56(d) declaration immediately explaining what specific facts you need and why, rather than just arguing the motion isn’t ripe.
The Partial Summary Judgment Option
One underused tool: partial summary judgment under Rule 56(a). You can target individual claims, defenses, or even specific elements. In a complex commercial case, knocking out two of five claims at summary judgment before trial dramatically simplifies the proceedings and can shift settlement dynamics. Courts appreciate the narrowing function, and it puts pressure on the opposing party’s case in ways a denial of a 12(b)(6) never does. Worth building into your pretrial strategy from the beginning, especially when paired with the court’s obligation under Rule 56(g) to identify undisputed facts even when full judgment isn’t granted.