Partial summary judgment and severability
 The appellants contend that the motion judge erred in granting partial summary judgment in circumstances where the issue before him was not severable from the remaining liability issues in the main action and counterclaim, both of which must go to trial.
 The issue determined by the motion judge was that the "Air-Supported Structure" was not completed by September 30, 2007, as required by the lease and, therefore, the respondents were entitled to terminate the lease pursuant to s. 3(a)(ii)(A). The appellants submit that this is the crucial, albeit not the only, issue in both the respondents' action and the appellants' counterclaim and that its resolution on a motion for summary judgment improperly precludes consideration of the issue at trial.
 Specifically, the appellants say that the balance of the respondents' claim for lost profits under the lease will require the trial court to determine whether WWK breached the lease. Similarly, the liability determination on WWK's counterclaim against the respondents will require a determination of whether it was the respondents who breached the lease. Given that this will require the trial court to determine whether the "Air-Supported Structure" was completed by September 30, 2007, the appellants argue that the motion judge improperly severed these issues by resolving them on the motion for summary judgment.
 I do not accept this submission. Rule 20 of the Rules of Civil Procedure, R.R.O. 1990, Reg. 194, specifically authorizes partial summary judgment:
20.01(1) A plaintiff may … move with supporting affidavit material or other evidence for summary judgment on all or part of the claim in the statement of claim. [Emphasis added.]
 In Ford Motor Co. of Canada Ltd. v. Ontario Municipal Employees Retirement Board (1997), 36 O.R. (3d) 384 (C.A.), Osborne J.A. identified three categories of cases in which a motion for partial summary judgment is appropriate. He described the first category in this fashion at pp. 394-95:
The cases in which summary judgment has been granted for "part of" a claim seem to me to fall into three groups:
(a) actions where the evidence establishes that there is no genuine issue for trial in respect of a discrete claim. These partial summary judgment cases require no further comment except to say the result of summary judgment for "part of" a claim is consistent with the purpose of Rule 20; the partial summary judgment removes a discrete issue from the issues to be tried and thus shortens the trial. This is consistent with "procedural justice" concerns referred to by Morden A.C.J.O. in Irving Ungerman and with the purpose of Rule 20 as referred to in Jockey Club... .
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