Medical - Consent and Capacity. Carmichael v. GlaxoSmithKline Inc.
In Carmichael v. GlaxoSmithKline Inc. (Ont CA, 2020) the Court of Appeal considered the issue of incapacity generally:
(iii) “Incapable”. Murray v. Alatishe
 Although s. 7(1)(a) does not define “incapable”, a person is generally said to be “incapable” if they lack physical or mental capabilities: Black’s Law Dictionary, Bryan A. Garner, ed., 10th ed. (St. Paul, Minn.: Thomson Reuters, 2014) (“incapacity”). As noted by Tulloch J.A. for a five-judge panel of this court in Ohenhen (Re), 2018 ONCA 65, at para. 81:
Generally, Ontario law provides that a person has the capacity to make a decision if they are able to understand the information that is relevant to making that decision and able to appreciate the reasonably foreseeable consequences of that decision or lack of decision: see e.g. Substitute Decisions Act, 1992, S.O. 1992, c. 30, ss. 6 (property decisions) and 45 (personal care decisions); Health Care Consent Act, [1996, S.O. 1996, c. 2, Sched. A] s. 4(1) (medical treatment); [R. v. Conception, 2014 SCC 60,  3 S.C.R. 82], at para. 22 (medical treatment). Capacity is linked to personal autonomy and a person’s self-determination and ability to make important life choices. Because of the importance of these values, courts generally set a low threshold for determining capacity: Calvert (Litigation Guardian of) v. Calvert (1997), 1997 CanLII 12096 (ON SC), 32 O.R. (3d) 281 (Gen. Div.), at p. 294, per Benotto J. (as she then was), aff’d 1998 CanLII 3001 (ON CA), 37 O.R. (3d) 221 (C.A.), leave to appeal refused,  S.C.C.A. 61; Ohenhen (Re), at para. 83.
 But the law also recognizes that a person’s capacity can vary with the decision at issue. Thus, “[a] person can be capable of making a basic decision and not capable of making a complex decision”: Calvert, at p. 293. As Tulloch J.A. stated in Ohenhen (Re), at para. 80: “a person may be capable of managing personal care, but not his or her finances. Or, a person may have the capacity to make a will for a simple estate, but not for a more complicated one.” In this regard, I agree with the observation of Benotto J. (as she then was) in Calvert, that the capacity to instruct counsel is at the higher end of the competency hierarchy, at p. 294:There is a distinction between the decisions a person makes regarding personal matters such as where or with whom to live and decisions regarding financial matters. Financial matters require a higher level of understanding. The capacity to instruct counsel involves the ability to understand financial and legal issues. This puts it significantly higher on the competency hierarchy. It has been said that the highest level of capacity is that required to make a will[.] [Emphasis added.]
In Murray v. Alatishe (Ont CA, 2019) the Court of Appeal stated the test for consent to medical treatment:
 Section 4(1) of the HCCA outlines a two-step test for capacity to consent to treatment: Starson v. Swayze, 2003 SCC 32 (CanLII),  1 S.C.R. 722, at para. 78. First, a person must be able to understand the information that is relevant to making a treatment decision. Second, a person must be able to appreciate the reasonably foreseeable consequences of the decision. This second element requires a person to be able to apply the relevant information to her own circumstances and to be able to weigh the foreseeable risks and benefits of a decision or lack thereof: Starson, at para. 78.