diff --git a/go/seatdef/callers.go b/go/seatdef/callers.go
index 177e4c16..ba60222d 100644
--- a/go/seatdef/callers.go
+++ b/go/seatdef/callers.go
@@ -101,6 +101,28 @@ func CallerEntryProblem(e string) string {
 		"holder:<seat>@same-node", e)
 }
 
+// DefaultCallers are the callers a verb that names none takes by its class (design 47 G §391): a read takes invokers,
+// persons and sessions; an act the operator and sessions; a warrant the operator. A verb that names no class is a
+// read.
+func DefaultCallers(class string) []string {
+	switch class {
+	case ClassAct:
+		return []string{CallerOperator, CallerSessions}
+	case ClassWarrant:
+		return []string{CallerOperator}
+	}
+	return []string{CallerInvokers, CallerPersons, CallerSessions}
+}
+
+// EffectiveCallers are the callers the verb is open to: the list it names, or the default of its class. A verb whose
+// callers are text, as the definitions before G wrote them, names no list and takes the default.
+func (v Verb) EffectiveCallers() []string {
+	if v.Callers != nil && !v.Callers.IsText() {
+		return v.Callers.List
+	}
+	return DefaultCallers(v.Class)
+}
+
 // The classes of a verb (design 47 G §391).
 const (
 	ClassRead    = "read"
diff --git a/go/seatdef/seatdef_test.go b/go/seatdef/seatdef_test.go
index abaa9720..206db19f 100644
--- a/go/seatdef/seatdef_test.go
+++ b/go/seatdef/seatdef_test.go
@@ -283,3 +283,22 @@ func TestAKeptEventsStreamIsNamedFromTheSeatAndTheEvent(t *testing.T) {
 		t.Errorf("the stream is %s", got)
 	}
 }
+
+// Design 47 G §391: a verb that names no callers takes its class's default, a verb that names them keeps them.
+func TestAVerbWithoutCallersTakesItsClassDefault(t *testing.T) {
+	for _, c := range []struct {
+		verb Verb
+		want string
+	}{
+		{Verb{}, "invokers persons sessions"},
+		{Verb{Class: ClassRead}, "invokers persons sessions"},
+		{Verb{Class: ClassAct}, "operator sessions"},
+		{Verb{Class: ClassWarrant}, "operator"},
+		{Verb{Class: ClassAct, Callers: &Callers{List: []string{"seat:mesh-broker"}}}, "seat:mesh-broker"},
+		{Verb{Class: ClassWarrant, Callers: &Callers{Text: "a person"}}, "operator"},
+	} {
+		if got := strings.Join(c.verb.EffectiveCallers(), " "); got != c.want {
+			t.Errorf("%+v is open to %q, want %q", c.verb, got, c.want)
+		}
+}
+}