have pleaded those facts in order to put the issue of the validity
of the acknowledgments before the court and did not raise any
limitation argument, made it an error for the motion judge to
find that the estate’s claim was statute-barred.
 This court explained in Beardsley v. Ontario (2001),
57 O.R. (3d) 1,  O.J. No. 4574 (C.A.), at para. 21, that
“[t]he expiry of a limitation period does not render a cause of
action a nullity; rather, it is a defence and must be pleaded”. See,
also, Strong v. Paquet Estate (2000), 50 O.R. (3d) 70,  O.J.
No. 2792 (C.A.), at paras. 35-37; Tran v. University of Western
Ontario,  O.J. No. 6645, 2016 ONCA 978, 410 D.L.R. (4th)
527, at para. 18; and Salewski v. Lalonde (2017), 137 O.R. (3d)
750,  O.J. No. 3188 (C.A.), at para. 43.
 There are two aspects to the statement from Beardsley.
One is that from a procedural fairness point of view, a plaintiff is
entitled to plead in response to a limitations defence, so that if
a motion is brought to dismiss the claim, the court will have all
the facts relied on to assess discoverability, or whatever other
factors a plaintiff may wish to raise in response: Beardsley,
at para. 22; Strong Estate, at para. 38; Metropolitan Toronto
Condominium Corp. No. 1352 v. Newport Beach Development
Inc. (2012), 113 O.R. (3d) 673,  O.J. No. 5682, 2012 ONCA
850, at paras. 115-16; and Greatrek Trust S.A./Inc. v. Aurelian
Resources Inc.,  O.J. No. 611, 2009 CarswellOnt 748
(S.C.J.), at para. 18.
 The requirement that an affirmative defence, including
a limitations defence, be pleaded to avoid surprise to the opposite party is reflected in rule 25.07(4) of the Rules of Civil Procedure, which provides:
25.07(4) In a defence, a party shall plead any matter on which the party
intends to rely to defeat the claim of the opposite party and which, if not
specifically pleaded, might take the opposite party by surprise or raise an
issue that has not been raised in the opposite party’s pleading.
 The second aspect of the statement from Beardsley, however, is more germane to this case. A limitations defence is “just
that, a defence”: Lacroix (Litigation guardian of) v. Dominique,
 M.J. No. 311, 2001 MBCA 122, 202 D.L.R. (4th) 121,
at para. 18. A defendant chooses whether or not to rely on a limitations defence, but is not obliged to do so: Graeme Mew, Debra
Rolph and Daniel Zacks, The Law of Limitations, 3rd ed. (
Toronto: LexisNexis, 2016), p. 166. See, e.g., Strong Estate, at paras. 35-
40; and Girsberger v. Kresz (2000), 50 O.R. (3d) 157,  O.J.
No. 4216 (C.A.), at para. 13.