Whether interpreting a testamentary trust or an inter vivos trust, the role of the court is purportedly the same – to implement the intent of the settlor:
When overseeing the administration of an estate, probate courts are primarily concerned with ascertaining and carrying out the testator’s intent. Courts have used a multiplicity of adjectives to express the importance of this task, describing it variously as “paramount,” “fundamental,” “cardinal,” “primary,” “overarching,” “controlling” “basic,” “proper,” and even as “the cornerstone,” “the touchstone,” or “the polestar” driving their duty, regardless of the unreasonableness or eccentricity of the will’s terms. Whether they call it interpretation, construction, or something else, most courts agree that, in dealing with the contents of a will, the initial step is to determine the testator’s intent at the time the will was executed. That determination employs the presumption that the testator knew the law in force at the time of such execution. After determining the testator’s intention, the court’s duty is to carry out that intention unless it is illegal, violates public policy, or is unconstitutional. This governing framework continues to be vaunted in recent will-interpretation jurisprudence as serving donative freedom, one of the core values of Anglo-American property law.
Oddly, under the Common Law the rules of construction that pertain to testamentary trusts are different from those that govern inter vivos trusts:
c. Trusts created by will. If a trust is created by will, the terms of the trust are determined by the provisions of the will as interpreted in light of all the relevant circumstances and direct evidence of intention in accordance with the general rules of law governing interpretation of wills.
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d. Trusts created inter vivos by written instrument. If a trust is created by a transaction inter vivos and is evidenced by a written instrument, the terms of the trust are determined by the provisions of the governing instrument as interpreted in light of all the relevant circumstances and such direct evidence of the intention of the settlor with respect to the trust as is not denied consideration because of a statute of frauds, the parol-evidence rule, or some other rule of law.
 Richard F. Storrow, Judicial Discretion and the Disappearing Distinction Between Will Interpretation and Construction, 56 Case W. Res. L. Rev. 65, 69-70 (2005). Although this statement of the importance of seeking and implementing the settlor’s intent is in the setting of testamentary transfers, it is equally applicable to inter vivos trusts. See Restatement (Third) of Trusts § 4.
 Restatement (Third) of Trusts § 4.