Torts - Damages - Mental Injury
Saadati v. Moorhead (SCC, 2017)
In this case the Supreme Court of Canada engages in a wide-ranging revision and clarification of the law of tort damages for mental injury, which is a must-read for anyone involved in such a case.
Firstly, on the issue of the specificity of pleadings required to ground a claim for damages for mental injury, the court stated:
 Drawing from the Court of Appeal’s statements regarding notice, the respondents argue that the trial judge’s award for mental injury was made in breach of procedural fairness, having no basis in the pleadings or submissions at trial. While I note that the respondents did not argue this point at the Court of Appeal, as the respondents now say and as the Court of Appeal said, cases should not be decided on grounds not raised (Insurance Corp. of British Columbia v. Patko, 2008 BCCA 65 (CanLII), 290 D.L.R. (4th) 687, at para. 37; Rodaro v. Royal Bank of Canada (2002), 2002 CanLII 41834 (ON CA), 59 O.R. (3d) 74 (C.A.), at para. 60; Burgsteden v. Long, 2014 SKCA 115 (CanLII), 378 D.L.R. (4th) 562, at para. 17; R. v. E.M.W., 2011 SCC 31 (CanLII),  2 S.C.R. 542, at para. 4). This rule is an instance of natural justice: each party is entitled to know and respond to the case that it must answer (Canada Trustco Mortgage Co. v. Renard, 2008 BCCA 343 (CanLII), 298 D.L.R. (4th) 216, at paras. 38-39).The court then continued to dispel any requirement that damages for mental injury be an aspect of a psychiatrically-recognized mental illness, and further to give mental injury damages largely the same standing in negligence law as physical damages, subject to the conventional elements of negligence [(1) duty, (2) breach of duty (3) damages and (4) causation] and a threshold test.:
 In claims for negligently caused mental injury, it is generally sufficient that the pleadings allege some form of such injury (Odhavji Estate v. Woodhouse, 2003 SCC 69 (CanLII),  3 S.C.R. 263, at para. 74). The appellant’s Statement of Claim alleges various injuries caused by the accident, including:
h) such further and other injuries as may become apparent through medical reports and examinations, details of which shall be provided as they become known;It also claims “general damages for pain and suffering, loss of earning capacity past, present and future, loss of opportunity, loss of enjoyment of life, loss of physical health . . .” (R.R., vol. I, at p. 7).
and the effects or results of the said injuries upon the Plaintiff include headaches, fatigue, dizziness, nausea and sleeplessness.
(R.R., vol. I, at p. 7)
B. Mental Injury
 Liability in negligence law is conditioned upon the claimant showing (i) that the defendant owed a duty of care to the claimant to avoid the kind of loss alleged; (ii) that the defendant breached that duty by failing to observe the applicable standard of care; (iii) that the claimant sustained damage; and (iv) that such damage was caused, in fact and in law, by the defendant’s breach (Mustapha, at para. 3). At issue here is the third element. As they argued at the Court of Appeal, the respondents say that the trial judge erred by awarding damages for mental injury that did not correspond to a proven, recognized psychiatric illness. More specifically, 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.
(1) Recovery for Mental Injury in Negligence Law
 The early common law’s posture towards claims for negligently caused mental harm was one of suspicion and sometimes outright hostility (McLoughlin v. O’Brian,  1 A.C. 410 (H.L.), at p. 433), and was “virtually programmed to entrench primitive suspicions and prejudices about ‘invisible’, intangible harm” (H. Teff, Causing Psychiatric and Emotional Harm: Reshaping the Boundaries of Legal Liability (2009), at p. 40). Mental injury was seen as “not derived through the senses, but [as] a product of the imagination” (Miner v. Canadian Pacific Railway Co. (1911), 18 W.L.R. 476 (Alta. S.C. en banc), at p. 478). This scepticism persisted into the last century, such that mental injury was not compensable unless accompanied by physical injury (see L. Bélanger-Hardy “Reconsidering the ‘Recognizable Psychiatric Illness’ Requirement in Canadian Negligence Law” (2013), 38 Queen’s L.J. 583, at pp. 599-600).
 While the absolute bar to recovery for mental injury absent physical injury was eventually lifted, the suspicion which originally impelled that bar persisted, and common law courts continued to impose conditions upon recovery beyond those applied to claims for negligently caused physical injury. While, therefore, in England liability for negligently caused mental injury was first recognized as early as 1901 (Dulieu v. White & Sons,  2 K.B. 669 (Div. Ct.)), it was conditional upon “a shock which arises from a reasonable fear of immediate personal injury to oneself” (p. 675), or (after Hambrook v. Stokes Brothers,  1 K.B. 141 (C.A.)), “a reasonable fear of immediate personal injury either to [the claimant, or the claimant’s children]” (p. 152). While recovery for mental injury in Canada remained parasitic to recovery for compensable physical injury well into the 20th century (e.g. Miner), by mid-century Canadian courts had also begun to permit recovery on similar conditions as English law — typically, on claimants having had at the material time a reasonable fear of physical injury to themselves or to their family (e.g. Horne v. New Glasgow, 1953 CanLII 335 (NS SC),  1 D.L.R. 832 (N.S.S.C.)).
 Further obstacles to recovery for mental injury arose in English law. In McLoughlin v. O’Brian, at pp. 419-21, Lord Wilberforce posited three considerations that could limit the boundaries of compensable “nervous shock”: the class of persons whose claims should be recognized (often referred to as relational proximity), the proximity of such persons to the accident (locational, or geographical proximity), and the means by which the “shock” is caused (temporal proximity) (G. H. L. Fridman, The Law of Torts in Canada (3rd ed. 2010), at p. 326). Where claimants alleged mental injury arising out of a sudden traumatic event, later judgments further distinguished between a “primary” victim (who was directly involved as a participant) and a “secondary” victim (who witnessed physical injuries caused to others) (see Alcock v. Chief Constable of South Yorkshire Police,  1 A.C. 310 (H.L.); and Page v. Smith,  1 A.C. 155 (H.L.)). This distinction has, however, sometimes proven difficult to apply in practice (as shown by the English law’s difficulty in categorizing the status of rescuers — see White v. Chief Constable of South Yorkshire Police,  2 A.C. 455 (H.L.)), and has been criticized as lacking foundation in principle, having no relevance to the justice of the claimant’s case (A. Beever, Rediscovering the Law of Negligence (2007), at pp. 405-7; J. Stapleton, “In Restraint of Tort”, in P. Birks, ed., The Frontiers of Liability (1994), vol. 2, 83, at p. 95; Mustapha v. Culligan of Canada Ltd. (2006), 2006 CanLII 41807 (ON CA), 84 O.R. (3d) 457 (C.A.), at para. 43). That this is so has never really been disputed. As Lord Hoffmann candidly acknowledged in White, “in this area of law, the search for principle was called off in Alcock . . . . No one can pretend that the existing law . . . is founded upon principle.”
 Other Commonwealth courts have taken a different path. The High Court of Australia expressly rejected the categories delineated by the House of Lords, preferring a more flexible foreseeability of harm test (Tame v. New South Wales,  HCA 35, 211 C.L.R. 317). In New Zealand, the primary/secondary victim distinction has not been definitively considered (S. Todd et al., The Law of Torts in New Zealand (5th ed. 2009), at pp. 182-84).
 Like the English courts, Canadian courts have occasionally struggled, as Professor Klar has described, “to find words which can clearly explain why, on the basis of arbitrary policy choices, certain types of claims seem to be too remote and uncompensable” (L. N. Klar, Tort Law (5th ed. 2012), at p. 505 (emphasis in original)). In Beecham v. Hughes (1988), 1988 CanLII 2839 (BC CA), 27 B.C.L.R. (2d) 1 (C.A.), and Rhodes v. Canadian National Railway (1990), 1990 CanLII 5401 (BC CA), 75 D.L.R. (4th) 248 (B.C.C.A.), for example, the multi-faceted proximity analysis formalized in McLoughlin v. O’Brian found favour. In Beecham, Lambert J.A. wrote (at p. 43):
. . . I would not put the entire emphasis on “causal proximity”, to the exclusion of “temporal proximity”, “geographical proximity” or “emotional proximity”. I would try to balance them all. A close but foreseeable emotional bond, as between a parent and child, may compensate, in the determination of the composite answer on liability, for a more remote causal proximity, as where the parent is not present when the child is injured. This Court has not, however, adopted either the primary/secondary victim distinction, or McLoughlin v. O’Brian’s disaggregated proximity analysis. Rather, in Mustapha, recoverability of mental injury was viewed (at para. 3) as depending upon the claimant satisfying the criteria applicable to any successful action in negligence — that is, upon the claimant proving a duty of care, a breach, damage, and a legal and factual causal relationship between the breach and the damage. Each of these elements can pose a significant hurdle: not all claimants alleging mental injury will be in a relationship of proximity with defendants necessary to ground a duty of care; not all conduct resulting in mental harm will breach the standard of care; not all mental disturbances will amount to true “damage” qualifiying as mental injury, which is “serious and prolonged” and rises above the ordinary emotional disturbances that will occasionally afflict any member of civil society without violating his or her right to be free of negligently caused mental injury (Mustapha, at para. 9); and not all mental injury is caused, in fact or in law, by the defendant’s negligent conduct.
 Indeed, the claim in Mustapha failed on that last element: the claimant’s damage was not caused in law by (that is, it was too remote from) the defendant’s breach. Mustapha thus serves as a salutary reminder that, even where a duty of care, a breach, damage and factual causation are established, there remains the pertinent threshold question of legal causation, or remoteness — that is, whether the occurrence of mental harm in a person of ordinary fortitude was the reasonably foreseeable result of the defendant’s negligent conduct (Mustapha, at paras. 14-16). And, just as recovery for physical injury will not be possible where injury of that kind was not the foreseeable result of the defendant’s negligence, so too will claimants be denied recovery (as the claimant in Mustapha was denied recovery) where mental injury could not have been foreseen to result from the defendant’s negligence.
 It follows that this Court sees the elements of the cause of action of negligence as furnishing principled and sufficient barriers to unmeritorious or trivial claims for negligently caused mental injury. The view that courts should require something more is founded not on legal principle, but on policy — more particularly, on a collection of concerns regarding claims for mental injury (including those advanced in this appeal by the intervener Insurance Bureau of Canada) founded upon dubious perceptions of, and postures towards, psychiatry and mental illness in general: that mental illness is “subjective” or otherwise easily feigned or exaggerated; and that the law should not provide compensation for “trivial matters” but should foster the growth of “tough hides not easily pierced by emotional responses” (A. M. Linden and B. Feldthusen, Canadian Tort Law (10th ed. 2015), at p. 449; R. Mulheron, “Rewriting the Requirement for a ‘Recognized Psychiatric Injury’ in Negligence Claims” (2012), 32 Oxford J. Leg. Stud. 77, at p. 82). The stigma faced by people with mental illness, including that caused by mental injury, is notorious (J. E. Gray, M. Shone and P. F. Liddle, Canadian Mental Health Law and Policy (2nd ed. 2008), at pp. 139 and 300-301), often unjustly and unnecessarily impeding their participation, so far as possible, in civil society. While tort law does not exist to abolish misguided prejudices, it should not seek to perpetuate them.
 Where, therefore, genuine factual uncertainty arises regarding the worthiness of a claim, this can and should be addressed by robust application of those elements by a trier of fact, rather than by tipping the scales via arbitrary mechanisms (R. Stevens, Torts and Rights (2007), at p. 56). Certainly, concerns about “subjective” symptoms or about feigned or exaggerated claims of mental injury are — like most matters of credibility — questions of fact best entrusted to the good sense of triers of fact, upon whose credibility determinations of liability and even of liberty often rest. In short, such concerns should be resolved by “a vigorous search for the truth, not the abdication of judicial responsibility” (Linden and Feldthusen, at p. 449; see also Toronto Railway Co. v. Toms (1911), 44 S.C.R. 268, at p. 276; Stevens, at p. 56).
 I add this. As to that first necessary element for recovery (establishing that the defendant owed the claimant a duty of care), it is implicit in the Court’s decision in Mustapha that 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).
 It is also implicit in Mustapha that the ordinary duty of care analysis is to be applied to claims for negligently caused mental injury. With great respect to courts that have expressed contrary views, it is in my view unnecessary and indeed futile to re-structure that analysis so as to mandate formal, separate consideration of certain dimensions of proximity, as was done in McLoughlin v. O’Brian. Certainly, “temporal”, “geographic” and “relational” considerations might well inform the proximity analysis to be performed in some cases. But the proximity analysis as formulated by this Court is, and is intended to be, sufficiently flexible to capture all relevant circumstances that might in any given case go to seeking out the “close and direct” relationship which is the hallmark of the common law duty of care (Cooper v. Hobart, 2001 SCC 79 (CanLII),  3 S.C.R. 537, at para. 32, citing Donoghue v. Stevenson,  A.C. 562 (H.L.), at pp. 580-81). As the Court has said, that analysis
focuses on factors arising from the relationship between the plaintiff and the defendant. . . .(2) Recognized Psychiatric Illness
. . .
As this Court stated in Hercules Managements Ltd. v. Ernst & Young, 1997 CanLII 345 (SCC),  2 S.C.R. 165, at para. 24, per La Forest J.:
The label “proximity”, as it was used by Lord Wilberforce in [Anns v. Merton London Borough Council,  A.C. 728 (H.L.)], was clearly intended to connote that the circumstances of the relationship inhering between the plaintiff and the defendant are of such nature that the defendant may be said to be under an obligation to be mindful of the plaintiff’s legitimate interests in conducting his or her affairs.(Cooper, at paras. 30 and 33 (emphasis in original))
 As I have already said, the principal issue presented by this appeal — and, in particular, by the Court of Appeal’s conclusion that the appellant’s claim failed for lack of expert evidence demonstrating a recognized psychiatric illness — concerns the element of the cause of action of negligence requiring the claimant to show damage. More specifically, it requires the Court to consider what constitutes mental injury, and how it may be proven.
 The origins of the putative requirement of showing a recognized psychiatric illness appear to lie in Lord Denning M.R.’s speech in Hinz v. Berry,  2 Q.B. 40 (C.A.), at p. 42:
In English law no damages are awarded for grief or sorrow caused by a person’s death. No damages are to be given for the worry about the children, or for the financial strain or stress, or the difficulties of adjusting to a new life. Damages are, however, recoverable for nervous shock, or, to put it in medical terms, for a recognisable psychiatric illness caused by the breach of duty by the defendant.This statement has been reiterated, albeit with some variation as to terminology. In McLoughlin v. O’Brian, at p. 431, for example, Lord Bridge described this hurdle as requiring “a positive psychiatric illness”. It has also been variously referred to as a “genuine”, “recognized” or “recognizable” psychiatric illness (Mulheron, at p. 81).
 Howsoever the term is phrased, it is far from clear on the text of Hinz v. Berry that it was intended to impose upon claimants the burden of showing a positive expert diagnosis. At the very least, it is not obvious that Hinz v. Berry sought to download to expert psychiatric witnesses the trier of fact’s task of determining whether the claimant sustained mental injury (Teff, at p. 53; and Bélanger-Hardy, at pp. 607-11). The respondents’ submission, therefore — that, by “recognizable psychiatric illness”, it was intended that mental injury be “recognizable” to a psychiatrically trained expert witness, and not to an ordinary witness — is founded upon a shaky premise.
 Despite some early resistance, however (e.g. McDermott v. Ramadanovic Estate (1988), 1988 CanLII 2840 (BC SC), 27 B.C.L.R. (2d) 45 (S.C.); Rhodes, per Southin J.A., concurring; Cox v. Fleming (1995), 1995 CanLII 3127 (BC CA), 15 B.C.L.R. (3d) 201 (C.A.); Mason v. Westside Cemeteries Ltd. (1996), 1996 CanLII 8113 (ON SC), 135 D.L.R. (4th) 361 (Ont. C.J. (Gen. Div.)); Flett v. Maxwell,  B.C.J. No. 1455 (QL) (Prov. Ct. (Civ. Div.)), Canadian trial and appellate courts after Hinz v. Berry began to see the requirement of a “recognizable psychiatric illness” as conditioning recovery for mental injury upon the claimant adducing expert testimony verifying a condition recognizable to the expert (e.g. Vanek v. Great Atlantic & Pacific Co. of Canada (1999), 1999 CanLII 2863 (ON CA), 48 O.R. (3d) 228 (C.A.), at paras. 65-67; Healey v. Lakeridge Health Corp., 2011 ONCA 55 (CanLII), 103 O.R. (3d) 401; Frazer v. Haukioja, 2010 ONCA 249 (CanLII), 101 O.R. (3d) 528; Kotai v. “Queen of the North” (The), 2009 BCSC 1405 (CanLII), 70 C.C.L.T. (3d) 221; Young v. Borzoni, 2007 BCCA 16 (CanLII), 277 D.L.R. (4th) 685; Graham v. MacMillan, 2003 BCCA 90 (CanLII), 15 C.C.L.T. (3d) 155; Koerfer v. Davies,  O.J. No. 1408 (QL) (C.A.); Duwyn v. Kaprielian (1978), 1978 CanLII 1271 (ON CA), 22 O.R. (2d) 736 (C.A.)). Similarly, despite some resistance elsewhere in the Commonwealth to restricting recovery for mental injury to claimants who can adduce such expert psychiatric evidence (N. J. Mullany and P. R. Handford, Tort Liability for Psychiatric Damage (1993), at p. 21), this threshold now prevails in the United Kingdom, Australia, and New Zealand (White, at p. 491; Tame, at paras. 193-94; van Soest v. Residual Health Management Unit,  NZCA 206,  1 N.Z.L.R. 179, at para. 65).
 In sum — and this is the state of the law which this Court must now evaluate — the law developed by Canadian lower courts (albeit, as I have mentioned, on an unstable premise) requires claimants alleging mental injury to show that such injury has manifested itself to an expert in psychiatry in the form of a clinically diagnosed, recognizable psychiatric illness. This has therefore “place[d] the categories of mental and emotional harm for which damages may be recovered in the hands of psychiatry. Whatever that discipline chooses to identify and name as a psychiatric illness becomes the law’s boundaries for damages in this area” (van Soest, at p. 205, per Thomas J., dissenting).
 Usually, this has been done with reference to what has been said to represent a “considerable degree of international agreement on the classification of mental disorders and their diagnostic criteria”, which are contained in the Diagnostic and Statistical Manual of Mental Disorders (“DSM”), published by the American Psychiatric Association, and the International Statistical Classification of Diseases and Related Health Problems (“ICD”), published by the World Health Organization (Mulheron, at p. 78, citing Sutherland v. Hatton,  EWCA Civ 76,  2 All E.R. 1, per Hale L.J. (as she then was); see also Bélanger-Hardy, at p. 586). The DSM, now in its 5th edition (2013), stipulates diagnostic criteria for, and classifies, mental disorders, while the ICD, now in its 10th revision (1992), contains statistically based classifications of all diseases (including “mental and behavioural disorders”).
 Confining compensable mental injury to conditions that are identifiable with reference to these diagnostic tools is, however, inherently suspect as a matter of legal methodology. While, for treatment purposes, an accurate diagnosis is obviously important, a trier of fact adjudicating a claim of mental injury is not concerned with diagnosis, but with symptoms and their effects (Mulheron, at p. 88). Put simply, there is no necessary relationship between reasonably foreseeable mental injury and a diagnostic classification scheme. As Thomas J. observed in van Soest (at para. 100), a negligent defendant need only be shown to have foreseen injury, and not a particular psychiatric illness that comes with its own label. In other words, the trier of fact’s inquiry should be directed to the level of harm that the claimant’s particular symptoms represent, not to whether a label could be attached to them. Downloading the task of assessing legally recoverable mental injury to the DSM and ICD therefore imports an arbitrary control mechanism upon recovery for mental injury, conditioning recovery not upon any legally principled basis directed to the alleged injury, but upon conformity with a legally irrelevant classification scheme designed to facilitate identification of particular conditions (L. Bélanger-Hardy, “Thresholds of Actionable Mental Harm in Negligence: A Policy-Based Analysis” (2013), 36 Dal. L.J. 103, at pp. 113-15; Mulheron, at pp. 87-88).
 Resort to the DSM or ICD in the context of litigating claims for mental injury has been variously rationalized as fostering objectivity, certainty and predictability of outcomes; and as preventing “indeterminate liability” (Tame, at paras. 193-94; Healey, at para. 65; Queen of the North, at para. 68). These rationalizations, however, do not withstand scrutiny. In particular, the putative objectivity, certainty and predictability said to be furnished by the recognizable psychological illness requirement are in my view overstated. Psychiatric diagnoses — like diagnoses of physical illness or injury — can sometimes be controversial even among treating practitioners (M. A. Jones, “Liability for Psychiatric Damage: Searching for a Path between Pragmatism and Principle”, in J. W. Neyers, E. Chamberlain and S. G. A. Pitel, eds., Emerging Issues in Tort Law (2007) 113, at p. 131). The categories identified in the DSM are, therefore, not static, and continue to be revised to reflect evolving psychiatric consensus on the classification of psychiatric disorders. Labels that were at one time widely accepted may become obsolete. The DSM (DSM-II), for example, identified homosexuality as a psychiatric disorder until 1973, after which it continued to identify “sexual orientation disturbance” for people “in conflict with” their sexual orientation. This was later replaced in the DSM-III with “ego-dystonic homosexuality”, which was itself removed in 1987 (J. Drescher, “Out of DSM: Depathologizing Homosexuality” (2015), 5 Behav. Sci. 565, at p. 571). The ICD retained homosexuality in its classification until 1990, and continues to identify ego-dystonic homosexuality as a recognized condition (although in 2014 the World Health Organization recommended its removal from its 11th revision, now in development) (S. Cochran et al., “Proposed declassification of disease categories related to sexual orientation in the International Statistical Classification of Diseases and Health Related Problems (ICD-11)” (2014), 92 Bull. World Health Organ. 672).
 Conversely, potential disorders originally excluded from the DSM may be “legitimized” by later inclusion. For example, “post-traumatic stress disorder” first appeared in the DSM (DSM-III) in 1980. And, with the publication of the DSM-IV, it no longer required “a psychologically traumatic event that is generally outside the range of usual human experience” (Jones, at p. 132). Similarly, the release of the 5th edition of the DSM (DSM-V) was preceded by a debate about the inclusion of grief as a psychiatric condition (R. A. Bryant, “Grief as a psychiatric disorder” (2012), 201 Br. J. Psychiatry 9, at pp. 9-10). Rather than fostering objectivity, certainty and predictability of outcomes, then, tethering determinations of legal liability to these iterative diagnostic tools relegates the law of negligence to following a sometimes meandering path as it is cleared by the cutting edge of au courant thinking in modern psychiatry — wherever it may lead, or from wherever it may retreat.
 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. Article 1457 of the Civil Code of Québec imposes a liability rule binding defendants “to make reparation for the injury, whether it be bodily, moral or material in nature” (see, e.g., Augustus v. Gosset, 1996 CanLII 173 (SCC),  3 S.C.R. 268, at para. 27). And yet, our attention has not been drawn to any instances where Quebec courts imposed liability that was in some way “indeterminate”. Further, and as I have explained is the case with unmeritorious or trivial claims for negligently caused mental injury, robust application of the elements of the cause of action of negligence should also be sufficient to address concerns for indeterminate liability. In particular, liability for mental injury must be confined to claims which satisfy the proximity analysis within the duty of care framework, which focuses on the relationship between the parties (Cooper, at para. 30), and the remoteness inquiry, which asks whether “the harm [is] too unrelated to the wrongful conduct to hold the defendant fairly liable” (Mustapha, at para. 12, quoting Linden and Feldthusen, at p. 360). We have been given no reason to suppose that the same sort of constraints which negligence law imposes upon claimants alleging physical injury would be less effective in weeding out unworthy claims for mental injury. It is therefore not only undesirable, but unnecessary to distort negligence law by applying the mechanism of a diagnostic threshold for proving mental injury.
 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.