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examination of the agreement as a whole is described as
doubt or as ambiguity or as uncertainty or as
difficulty of construction.
The types of extrinsic evidence that will be admitted,
if they meet the test of relevance and are not excluded
by other evidentiary tests, include evidence of the
facts leading up to the making of the agreement,
evidence of the circumstances as they exist at the time
the agreement is made and, in Canada, evidence of
subsequent conduct of the parties to the agreement.
However, to say that these types of evidence become
admissible where two reasonable interpretations exist
is not to say that the evidence, if tendered, must be
given weight. In the case of evidence of subsequent
conduct, the evidence is likely to be most cogent where
the parties to the agreement are individuals, the acts
considered are the acts of both parties, the acts can
relate only to the agreement, the acts are intentional
and the acts are consistent only with one of the
alternative interpretations. Where the parties to the
agreement are corporations and the acts are the acts of
employees of the corporations, then evidence of
subsequent conduct is much less likely to carry weight.
In no case is it necessary that weight be given to
evidence of subsequent conduct. In some cases it may
be most misleading to do so, and it is to this danger
that allusions are made throughout the recent English
cases, particularly L. Schuler AG v. Wickman Machine
Tool Sales Ltd., supra, and James Miller & Partners
Ltd. v. Whitworth Street Estates (Manchester) Ltd.,
supra. In England the risks have been considered
sufficiently grave that the possibility of illumination
from the use of subsequent conduct has been ruled out.
In Canada they have not, but those risks must be
carefully assessed in each individual case before
determining to give weight to subsequent conduct."
386.
387.
At page 377, Craig, J.A. said:
"The law of Canada does permit subsequent conduct to be
used as an aid in construing a contract if, but only
if, the contract is ambiguous in some respect."
In B.C. Hydro and Power Authority v. Cominco Ltd. (1989), 34
B.C.L.R. (2d) 60 (C.A.), the Court said at page 74: