diff --git a/tag/tag.go b/tag/tag.go
index 4818914..dff7ce5 100644
--- a/tag/tag.go
+++ b/tag/tag.go
@@ -42,10 +42,11 @@ type Tag struct {
    Aliases []string
 
 
-   // TODO: define an actual TagSet type for this kind of functionality?
-   // Parents maps 'canonical' (human readable) tag names to their normalised (path friendly) form. It is implemented as
-   // a map rather than a simple slice to essentially act as a set, with the normalised forms being just a convenience.
-   Parents map[string]string
+   // Parents is a set of Tags that can be considered to be directly 'above' this tag in a perceptual hierarchy. It is
+   // probably best to lean on the broad side when considering what conceptually constitutes a 'parent'. For example,
+   // 'mathematics' could be considered a parent of 'algebra', 'geometry', etc. but also 'physics', 'engineering', even
+   // 'music'.
+   Parents sets.Set[string]
 
    // Children ?
 
@@ -220,9 +221,9 @@ func (t *Tag) UnmarshalYAML(value *yaml.Node) error {
       t.Icon = icon.(string)
    }
    if parents, ok := data["parents"]; ok {
-      t.Parents = map[string]string{}
+      t.Parents = sets.New[string]()
       for _, p := range parents.([]any) {
-         t.Parents[p.(string)] = normaliseName(p.(string))
+         t.Parents.Insert(p.(string))
       }
    }
    if relations, ok := data["relations"]; ok {
diff --git a/tag/tag_test.go b/tag/tag_test.go
index c512e50..eea0c51 100644
--- a/tag/tag_test.go
+++ b/tag/tag_test.go
@@ -29,6 +29,10 @@ func Test_LoadPath(t *testing.T) {
 func Test_normaliseName(t *testing.T) {
    assert.Equal(t, "test-tag-name", normaliseName("Test TAG name"))
    assert.Equal(t, "already-normalised", normaliseName("already-normalised"))
+   tags, _ := LoadAll()
+   for name, _ := range tags {
+      t.Logf("tag: %v", name)
+   }
  }
 
 
@@ -56,10 +60,10 @@ func Test_MarshalYAML(t *testing.T) {
             "QWERTYUIOP",
             "ASDFGHJKLZ",
          ),
-         Parents: map[string]string {
-            "Parent 1": "parent-1",
-            "Parent Number Two": "parent-number-two",
-         },
+         Parents: sets.New(
+            "Parent 1",
+            "Parent Number Two",
+         ),
          Relations: map[string]string {
             "Relation 1": "similar subject",
             "Relation Number Two": "first encountered in the same book",
@@ -101,10 +105,10 @@ func Test_UnmarshalYAML(t *testing.T) {
             "QWERTYUIOP",
             "ASDFGHJKLZ",
          ),
-         Parents: map[string]string {
-            "Parent 1": "parent-1",
-            "Parent Number Two": "parent-number-two",
-         },
+         Parents: sets.New(
+            "Parent 1",
+            "Parent Number Two",
+         ),
          Relations: map[string]string {
             "Relation 1": "similar subject",
             "Relation Number Two": "first encountered in the same book",