Even though truth or falsehood is predicated of assertions in ways slightly different from other speech acts, Graeme Goldsworthy (citing G. Allison) notes an important caveat: “Every speech-act raises the question of the truth or falsity of the referring expression and of the predicating expression. The force does not affect the referring expression, but it does affect the predication” (Gospel-Centered Hermeneutics, pg. 212).
In his Inerrancy and the Gospels: A God-Centered Approach to the Challenges of Harmonization (Crossway, 2012), Vern Poythress unpacks this concept in a very accessible way:
When we say that God speaks truthfully and that his speech can be trusted, we are including all of his speech. His speech includes instances where he makes specific assertions, but also other kinds of speech.
People sometimes use the word true in a narrow sense to describe the truth of assertions, in distinction from commands, requests, questions, wishes, and longer, complex discourses. For example, Jill may say, “The door is open.” In this context, “The door is open” is an assertion. It is true or false, depending on the position of the door. But suppose Jill says, “Please open the door.” We would not normally say that her request is “true.” Nevertheless, requests, questions, and longer discourses usually also imply commitments on the part of the speaker to various related statements. Jill implies that the door is not yet open, or at least not fully open. Consider the command “You shall not steal” in Exodus 20:15. Though not an assertion, it implies a number of assertions. It implies (1) that stealing is wrong, (2) that God says, “You shall not steal,” and (3) that God does not approve of stealing. All of these implications are true.
Longer discourses like the Gospels contain parables of Jesus, and these have to be received for what they are—as parables—if we are going to appreciate their truth properly. Parables imply truths about the kingdom of God, but such implications must be sought out by appreciating how parables do their job. When we say that God’s speech is always truthful, we should endeavor to preserve the richness of his speech and not insist that only some kinds of discourse or only some pieces within a discourse have authority over us.
Inerrancy and the Gospels, pg. 28. (Bold emphasis added.)
Poythress also includes this useful footnote concerning the import of Psalm 119: “Frame, Doctrine of the Word of God, makes clear that God’s authority belongs to all aspects of his speech, including questions and commands as well as statements. Ps. 119:151 says, ‘All your commandments are true,’ applying the word ‘true’ to commandments, not merely assertions. This kind of use shows the appropriateness of using the word ‘true’ with respect to communications of other kinds besides assertions” (Inerrancy and the Gospels, pg. 28, n.3).
R. Andrew Compton
Christ Reformed Church (URCNA)