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The testator gave a large sum of money in his Will to certain of his friends, stating that they should hold it on trust for purposes that he would communicate to them. The question that arose was whether the trust obligation was binding on the 'trustees'. This arrangement was not asecret trust, since the existence of the trust and the identity of the trustees was specified -- it was what is now called ahalf secret trust.

The House of lords held that, in principle, a trust of this meta would be enforceable by the beneficiaries, despite that it allows the testator to bypass the wills act (1837) and make unattested posthumous dispositions of his property. The doctrinal reasons that were offered for enforcing a half-secret trusts were questionable (see SecretAndHalfSecretTrusts), but it now appears settled law that they are enforceable.

In fact, the trust in Blackwell was not enforced, because it was not clear that the terms of the trust had been impressed on the trustees by the time the will was executed. Viscount Sumner pointed out that the courts would not allow a testator to reserve the right to make future unattested dispositions. Of course, because in a fully-secret trust the testator can do exactly that, there is no logical basis for this rule (again, see secret and half secret trusts for a discussion of this point).

• Mentioned in METCALF v. BLACK DOG REALTY, LLC