Introduction

In the wake of the Supreme Court of Canada’s decision in Grant Thornton LLP v. New Brunswick, 2021 SCC 31[1], civil litigators across the country are reassessing the way limitation periods are understood, calculated, and applied. While the case dealt specifically with an auditor’s liability to a provincial government, its reasoning on “discoverability” has broad implications. For Ontario motor vehicle accident litigants, particularly those asserting that their injuries meet the statutory threshold under the Insurance Act[2], the ruling may fundamentally alter when the two-year limitation period begins to run.

For years, plaintiffs in motor vehicle accident cases have relied on the idea that the limitation period doesn’t truly begin until they have expert confirmation that their injuries meet the threshold of a “permanent serious impairment of an important physical, mental or psychological function.” In practice, this has meant waiting for specialist reports, chronic pain assessments, or long-term functional testing before commencing tort actions. But Grant Thornton calls this approach into question. The Court emphasized that it is not legal certainty or a formal medical opinion that triggers the limitation period—it is the plaintiff’s knowledge of the material facts that allow for a plausible inference of liability.

This blog explores the potential application of Grant Thornton in Ontario car accident litigation, with a focus on when plaintiffs are deemed to have discovered that their injuries meet the threshold. Through five real-world scenarios, we illustrate how the discoverability standard articulated in Grant Thornton may catch some plaintiffs off-guard and force counsel to reassess their timelines.

I. The Discoverability Standard Post-Grant Thornton

At the core of the Grant Thornton decision is a clear and streamlined formulation of when a civil claim is discoverable. According to Justice Moldaver, a claim is discovered when the plaintiff has actual or constructive knowledge of the material facts that give rise to a plausible inference of liability.

Applied to motor vehicle accident cases, this means plaintiffs don’t need to be told by an orthopaedic surgeon, neurologist, or psychologist that they will never fully recover. What they need is knowledge that:

1. 1. They have suffered a loss or injury;
   2. The injury was caused by the accident; and
   3. The injury has had a serious and lasting impact on their life.

The Court emphasized that knowledge of every legal element of a cause of action is not necessary. What matters is whether the plaintiff can reasonably connect the dots between their injuries and the potential for liability. This makes the analysis more fact-driven and less dependent on formal medical assessments.

II. The Threshold Test in Ontario Tort Claims

Under s. 267.5(5) of the Insurance Act, plaintiffs in Ontario cannot recover general damages for pain and suffering unless they meet a defined threshold:

“…the plaintiff must have sustained a permanent serious impairment of an important physical, mental or psychological function.”

This threshold is both medical and functional. It is often a point of contention in tort claims, particularly in soft-tissue and chronic pain cases. Plaintiffs and their counsel have traditionally treated the threshold as a moving target, with the belief that the limitation period doesn’t start until they “know” the threshold is met.

But Grant Thornton undermines this assumption. It clarifies that plaintiffs don’t need a legal or expert conclusion—they just need sufficient knowledge of the material facts that support the inference. Once a plaintiff understands that they are injured, that the injury continues to interfere with their life, and that the accident caused it, the limitation period may be considered to have begun.

III. Scenario One: The Wait-for-a-Specialist Trap

Jasmin, age 34, is rear-ended while stopped at a red light. She is taken to the ER and diagnosed with whiplash and soft tissue injuries. She undergoes physiotherapy for several months, but her neck pain persists. She can’t sleep comfortably, stops attending yoga, and takes a leave from her warehouse job due to pain. She tells her GP that she doesn’t feel like her old self. Her GP refers her to a chronic pain specialist, but the earliest available appointment is 13 months later. She consults a lawyer 18 months after the accident, who tells her to wait for the chronic pain report before issuing a statement of claim.

This is a common scenario. Pre-Grant Thornton, the lawyer may have reasonably believed the limitation period hadn’t started. But under the new framework, Jasmin likely knew, or ought to have known, by month 6 or 9 that her injuries were persistent, life-altering, and serious. The fact that she stopped working, curtailed daily activities, and described ongoing dysfunction to her doctor would arguably trigger a plausible inference of liability. Waiting for a specialist’s report could jeopardize her claim.

IV. Scenario Two: The “I Thought I’d Get Better” Defence

Ahmed, a 58-year-old cab driver, is struck on the driver’s side by a speeding SUV. He walks away from the accident and initially refuses treatment. Over the next three months, he experiences increasing pain in his hip and back. He continues working but takes more breaks. By month 9, he reduces his hours by half and eventually stops driving. He mentions to a friend that he’s “never felt right since the crash,” but doesn’t consult a lawyer until year three.

Under Grant Thornton, Ahmed’s subjective belief that he might get better does not pause the limitation clock. Courts will look at when he knew or ought to have known the impact was serious and long-lasting. His gradual deterioration, cessation of work, and acknowledgment to others of ongoing pain may suffice to start the limitation period. Ignorance of legal remedies is not an excuse.

V. Scenario Three: Psychological Injuries and Inference

Laura, a university student, is a pedestrian hit in a crosswalk. She breaks her arm and is treated promptly. Physically, she recovers. But over the next year, she suffers panic attacks, insomnia, and eventually drops out of school. She sees her GP who prescribes medication but does not diagnose PTSD. She waits two years and three months before commencing a tort action.

In psychological injury cases, diagnosis is often delayed or uncertain. But under Grant Thornton, what matters is whether Laura had enough material facts to infer a serious, lasting impairment. The inability to resume studies, ongoing anxiety, and daily disruption may be sufficient to trigger the limitation period, even in the absence of a formal psychiatric diagnosis. Plaintiffs with mental health injuries must act cautiously.

VI. Scenario Four: Mild Traumatic Brain Injury (mTBI)

Ben, a 42-year-old project manager, is involved in a highway collision. He hits his head but remains conscious. Over time, he reports fogginess, memory lapses, and difficulty concentrating. His employer notices performance issues. At month 15, he is terminated. He sees a neuropsychologist at month 20 who confirms mTBI. His lawyer issues a statement of claim at month 28.

Here again, Grant Thornton changes the calculus. Ben was aware of cognitive decline and its impact on work well before the neuropsychological report. While expert evidence strengthens the claim, it is not a precondition to starting the clock. The combination of subjective symptoms, employer observations, and job loss may support a plausible inference that the injuries are serious and potentially permanent.

VII. Scenario Five: Pre-Existing Conditions and Delay in Attribution

Rose, age 67, has pre-existing arthritis and depression. She is involved in a T-bone collision and suffers bruising, exacerbated joint pain, and increased fatigue. Over 18 months, her functional capacity deteriorates. She assumes it is “just aging.” Her family doctor suggests the accident may have worsened her condition. Her lawyer issues the claim at month 26.

This is a textbook case of delayed attribution. But under Grant Thornton, once Rose knew her condition had worsened post-accident, and that her quality of life had declined meaningfully, the claim may have been discoverable. The existence of pre-existing conditions does not delay discoverability if the plaintiff is aware of a material worsening that can be linked to the accident.

VIII. Implications for Plaintiffs and Counsel

These scenarios all highlight a stark reality: plaintiffs who assume that formal diagnoses, specialist opinions, or wait-and-see approaches will pause the limitation clock are at risk. Grant Thornton makes clear that it is knowledge of facts, not opinions, that starts the clock. Functional losses, persistent symptoms, interference with employment or daily activities—these are sufficient to support a plausible inference.

For plaintiff counsel, this means being more aggressive about documentation, earlier in the process. Waiting for a full clinical picture may now be a liability. Intake processes must probe not just when the accident happened, but when the client knew they were not recovering. Standard retainer letters should be updated to reflect this risk.

For defence counsel, Grant Thornton offers a sharpened tool to challenge late claims. Examination for discovery questions should focus on when the plaintiff first noticed ongoing symptoms, what they told their doctor, and what impact the injuries had on daily functioning.

IX. Case Law Trends to Watch

Ontario courts have not yet fully reckoned with the implications of Grant Thornton in the motor vehicle context, but the groundwork is being laid. Post-2021 decisions may increasingly reference the standard of “plausible inference” rather than requiring confirmation of threshold via expert report. Defence motions for summary judgment based on expired limitation periods may rise in frequency.

One area of tension will be whether the threshold analysis under the Insurance Act remains a predominantly legal test requiring expert input, or whether it becomes a factual assessment driven by the plaintiff’s own lived experience. If courts adopt the Grant Thornton reasoning wholesale, the emphasis will be on what the plaintiff subjectively and objectively knew—not what they were told by a doctor.

X. The Next Trap? How Ontario’s Proposed Upfront Evidence Model Could Complicate Limitation Period Analysis

Ontario’s civil justice system is on the brink of transformation. Among the most debated reforms under consideration is the introduction of a UK-style upfront evidence and pre-claim disclosure regime. Under this model, plaintiffs would be required to compile and disclose significant supporting evidence—often including medical records, expert reports, and damages documentation—before commencing a claim. The goal is admirable: to encourage early resolution, streamline litigation, and reduce procedural gamesmanship. But in light of Grant Thornton, this reform raises a troubling paradox for personal injury plaintiffs.

Under Grant Thornton, the limitation period begins to run not when the plaintiff has expert confirmation, but when they have—or ought reasonably to have—knowledge of material facts giving rise to a plausible inference of liability. This means that the clock may be ticking well before a plaintiff has assembled the very documentation the new procedural rules may soon require before issuing a claim.

This disconnect could lead to a dangerous new trap: a plaintiff may know enough to start the limitation period under Grant Thornton, but not yet possess the evidentiary record required to comply with a mandatory pre-claim disclosure rule. In threshold cases involving chronic pain, psychological injury, or delayed attribution to pre-existing conditions, the evidentiary file often trails behind the factual reality of impairment. Plaintiffs would then face a dilemma—risk missing the limitation deadline by waiting to collect upfront evidence, or rush to file prematurely without the documentation needed to meet procedural compliance.

Plaintiff-side counsel must be prepared to confront this timing conflict head-on. Intake procedures will need to evolve. Advising clients to wait for a full medical picture may be malpractice in a post-Grant Thornton world—particularly if procedural reforms raise the bar for what must be filed on day one. Defence counsel, meanwhile, may have new tools to argue that a plaintiff’s claim is both late and procedurally defective.

If Ontario moves forward with a front-loaded litigation model, it will need to reconcile this with the Supreme Court’s discoverability standard. Clear rules will be essential. Without legislative or judicial guidance, the tension between discoverability and disclosure could leave injury claimants trapped between a ticking limitation clock and an evidentiary burden they can’t yet meet.

XI. Conclusion: The Clock Starts Sooner—And the Road Just Got Narrower

The Supreme Court’s decision in Grant Thornton LLP v. New Brunswick has redrawn the discoverability map. While the test is now clearer—focusing on when a plaintiff knows enough to draw a plausible inference of liability—it is also less forgiving. For Ontario motor vehicle accident victims, this should be a wake-up call. The era of waiting for medical certainty or formal diagnosis is over. Once a plaintiff knows they are injured, that the injury is persistent, and that it is materially affecting their life, the limitation clock may already be ticking.

But that’s not the only trap. With Ontario now contemplating a shift to a UK-style upfront evidence model—where claimants must compile and disclose substantial supporting documentation before filing—plaintiffs could soon find themselves caught between two conflicting timelines. They may know enough to trigger the limitation period under Grant Thornton, yet still lack the documentation required to commence a claim under a reformed procedural regime.

Personal injury lawyers must now operate on two fronts: assessing discoverability risk earlier and preparing evidentiary records faster. Intake protocols, limitation tracking, and retainer letters all need to be recalibrated for this new landscape. Delay is no longer just dangerous—it may soon be procedurally fatal. Plaintiffs need legal advice not just promptly—but proactively. Because in the post-Grant Thornton, pre-action disclosure era, time isn’t just of the essence—it’s the whole case.