Sometimes a trust, such as a testamentary trust, is written in such a way that it cannot be fulfilled, either because of the confusing vocabulary used or changed circumstances.
As Mulheron wrote in her 2006 treatise:
"... stated in its simplest terms, the cy-près doctrine is the vehicle by which the intentions of the donor (settlor or testator) may be given effect 'as nearly as possible' in circumstances where literal compliance with the donor's stated intentions cannot be effectuated."
In the presence of such a situation, the Court has the power to interpret the trust document as nearly as possible in light of the intention of the settlor, especially where a literal construction would give the document illegal, impracticable or impossible effect.
"Where a clear charitable intention is expressed, it will not be permitted to fail because the mode, if specified, cannot be executed, but the law will substitute another mode cy-près, that is, as near as possible to the mode specified by the donor."1
The power:
"... seems to have been borrowed from the Roman law; for by that law, donations for public purposes were sustained and were applied, when illegal, cy-près,to other purposes, at least one hundred years before Christianity became the religion of the empire".2
References:
1. Boy Scouts of Canada, Provincial Council of Newfoundland v. Doyle (1997) 151 Nfld. & PEIR 91 (Newfoundland Court of Appeal)
2. Story, Joseph, Equity Jurisprudence, 1988, The Legal Classics Library, Birmingham, Alabama.
Duhaime, Lloyd, Duhaime on Trusts: Charitable Trusts, published at duhaime.org/LegalResources/ElderLawWillsTrustsEstates/tabid/349/articleType/ArticleView/articleId/340/Charitable-Trusts.aspx
Mulheron, Rachael, The Modern Doctrine of Cy-près (London: University College London Press, 2006).