In a ground-breaking decision released today, the Supreme Court of Canada in Saadati v. Moorhead, 2017 SCC 28, overturned the BC Court of Appeal and held that the finding of legally compensable mental injury need not rest, in whole or in part, on the claimant proving a recognized psychiatric injury. The court held:
 ...the Court must answer the narrow question of whether it is strictly necessary, in order to support a finding of legally compensable mental injury, for a claimant to adduce expert evidence or other proof of a recognized psychiatric illness.
 ... Canadian negligence law recognizes that a duty exists at common law to take reasonable care to avoid causing foreseeable mental injury, and that this cause of action protects a right to be free from negligent interference with one’s mental health. That right is grounded in the simple truth that a person’s mental health — like a person’s physical integrity or property, injury to which is also compensable in negligence law — is an essential means by which that person chooses to live life and pursue goals (A. Ripstein, Private Wrongs (2016), at pp. 87 and 252-53). And, where mental injury is negligently inflicted, a person’s autonomy to make those choices is undeniably impaired, sometimes to an even greater degree than the impairment which follows a serious physical injury (Bourhill v. Young,  A.C. 92 (H.L.), at p. 103; Toronto Railway, at p. 276). To put the point more starkly, “[t]he loss of our mental health is a more fundamental violation of our sense of self than the loss of a finger” (Stevens, at p. 55).
 The view that a recognizable psychiatric illness requirement is necessary to prevent indeterminate liability, advanced before us by the respondents and the Insurance Bureau of Canada, is similarly untenable...
 In short, no cogent basis has been offered to this Court for erecting distinct rules which operate to preclude liability in cases of mental injury, but not in cases of physical injury. Indeed, there is good reason to recognize the law of negligence as already according each of these different forms of personal injury — mental and physical — identical treatment. As the Court observed in Mustapha (at para. 8), the distinction between physical and mental injury is “elusive and arguably artificial in the context of tort”. Continuing (and citing Page v. Smith, at p. 188), the Court explained that, “[i]n an age when medical knowledge is expanding fast, and psychiatric knowledge with it, it would not be sensible to commit the law to a distinction between physical and psychiatric injury, which may . . . soon be altogether outmoded. Nothing will be gained by treating them as different ‘kinds’ of personal injury, so as to require the application of different tests in law” (emphasis in original; see also S. Deakin, A. Johnston and B. Markesinis, Markesinis and Deakin’s Tort Law (7th ed. 2013), at p. 124). This is entirely consistent with the Court’s longstanding view, expressed over a century ago, by Fitzpatrick C.J. in Toronto Railway, at pp. 269-70:
It would appear somewhat difficult to distinguish between the injury caused to the human frame by the impact and that resulting to the nervous system in consequence of the shock . . . . The nature of the mysterious relation which exists between the nervous system and the passive tissues of the human body has been the subject of much learned speculation, but I am not aware that the extent to which the one acts and reacts upon the other has yet been definitely ascertained. . . . I cannot find the line of demarcation between the damage resulting to the human [body] . . . and that which may flow from the disturbance of the nervous system . . . . The latter may well be the result of a derangement of the relation existing between the bones, the sinews, the arteries and the nerves. In any event the resultant effect is the same. The victim is incapacitated . . . .
Or, as Davies J. (as he then was) added in Toronto Railways (at p. 275), “[t]he nervous system is just as much a part of man’s physical being as the muscular or other parts”. In a similar vein, Lord Macmillan, in Bourhill v. Young (at p. 103), said “[t]he distinction between mental shock and bodily injury was never a scientific one, for mental shock is presumably in all cases the result of, or at least accompanied by, some physical disturbance in the sufferer’s system.”
 It follows that requiring claimants who allege one form of personal injury (mental) to prove that their condition meets the threshold of “recognizable psychiatric illness”, while not imposing a corresponding requirement upon claimants alleging another form of personal injury (physical) to show that their condition carries a certain classificatory label, is inconsistent with prior statements of this Court, among others. It accords unequal — that is, less — protection to victims of mental injury. And it does so for no principled reason (Beever, at p. 410). I would not endorse it.
 None of this is to suggest that mental injury is always as readily demonstrable as physical injury. While allegations of injury to muscular tissue may sometimes pose challenges to triers of fact, many physical conditions such as lacerations and broken bones are objectively verifiable. Mental injury, however, will often not be as readily apparent. Further, and as Mustapha makes clear, mental injury is not proven by the existence of mere psychological upset. While, therefore, tort law protects persons from negligent interference with their mental health, there is no legally cognizable right to happiness. Claimants must, therefore, show much more — that the disturbance suffered by the claimant is “serious and prolonged and rise[s] above the ordinary annoyances, anxieties and fears” that come with living in civil society (Mustapha, at para. 9). To be clear, this does not denote distinct legal treatment of mental injury relative to physical injury; rather, it goes to the prior legal question of what constitutes “mental injury”. Ultimately, the claimant’s task in establishing a mental injury is to show the requisite degree of disturbance (although not, as the respondents say, to show its classification as a recognized psychiatric illness).
 Nor should any of this be taken as suggesting that expert evidence cannot assist in determining whether or not a mental injury has been shown. In assessing whether the claimant has succeeded, it will often be important to consider, for example, how seriously the claimant’s cognitive functions and participation in daily activities were impaired, the length of such impairment and the nature and effect of any treatment (Mulheron, at p. 109). To the extent that claimants do not adduce relevant expert evidence to assist triers of fact in applying these and any other relevant considerations, they run a risk of being found to have fallen short. As Thomas J. observed in van Soest (at para. 103), “[c]ourts can be informed by the expert opinion of modern medical knowledge”, “without needing to address the question whether the mental suffering is a recognisable psychiatric illness or not”. To be clear, however: while relevant expert evidence will often be helpful in determining whether the claimant has proven a mental injury, it is not required as a matter of law. Where a psychiatric diagnosis is unavailable, it remains open to a trier of fact to find on other evidence adduced by the claimant that he or she has proven on a balance of probabilities the occurrence of mental injury. And, of course, it also remains open to the defendant, in rebutting a claim, to call expert evidence establishing that the accident cannot have caused any mental injury, or at least any mental injury known to psychiatry. While, for the reasons I have given, the lack of a diagnosis cannot on its own be dispositive, it is something that the trier of fact can choose to weigh against evidence supporting the existence of a mental injury.
The full decision can be found here: https://scc-csc.lexum.com/scc-csc/scc-csc/en/item/16664/index.do