What is a duty to defend in a personal injury policy where a loss arises from a loss arising from several causes?

Where a loss arises from several causes, some of which fall within coverage and some of which are not covered, there is a duty to defend absent clear exclusory language denying coverage for multiple independent concurrent causes or ‘mixed claims’: Derksen v. 539938 Ontario Ltd., 2001 SCC 72, [2001] 3 SCR 398, at para. 48. This is because, as noted by Doherty J.A. in Hanis, at para. 23: I see no unfairness to the insurer in holding it responsible for all reasonable costs related to the defence of covered claims if that is what is provided for by the language of the policy. If the insurer has contracted to cover all defence costs relating to a claim, those costs do not increase because they also assist the insured in the defence of an uncovered claim. The insurer's exposure for liability for defence costs is not increased. Similarly, the insured receives nothing more than what it bargained for – payment of all defence costs related to a covered claim.