diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..b9f67eb
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,20 @@
+package orm
+
+import (
+	"errors"
+)
+
+var (
+	ErrNotASlice               = errors.New("Current object or field is not a slice!")
+	ErrNotAStruct              = errors.New("Current object or field is not a struct!")
+	ErrOutOfBounds             = errors.New("Index(es) out of bounds!")
+	ErrAppendMultipleDocuments = errors.New("Cannot append to multiple documents!")
+	ErrNotSliceOrStruct        = errors.New("Current object or field is not a slice nor a struct!")
+)
+
+const (
+	errFmtMalformedField     = "Malformed field name passed: '%s'"
+	errFmtNotAModel          = "Type '%s' is not a model"
+	errFmtNotHasID           = "Type '%s' does not implement HasID"
+	errFmtModelNotRegistered = "Model not registered for type: '%s'"
+)
diff --git a/model.go b/model.go
index 0b4163f..3cd3917 100644
--- a/model.go
+++ b/model.go
@@ -259,7 +259,7 @@ func (m *Model) Append(field string, a ...interface{}) error {
 		fv = fv.Elem()
 	}
 	if fv.Kind() != reflect.Slice {
-		return fmt.Errorf("Current object is not a slice!")
+		return ErrNotASlice
 	}
 	for _, b := range a {
 		val := reflect.ValueOf(incrementTagged(b))
@@ -291,7 +291,7 @@ func (m *Model) Pull(field string, a ...any) error {
 		fv = fv.Elem()
 	}
 	if fv.Kind() != reflect.Slice {
-		return fmt.Errorf("Current object is not a slice!")
+		return ErrNotASlice
 	}
 outer:
 	for _, b := range a {
@@ -332,7 +332,7 @@ func (m *Model) Swap(field string, i, j int) error {
 		return err
 	}
 	if i >= fv.Len() || j >= fv.Len() {
-		return fmt.Errorf("index(es) out of bounds")
+		return ErrOutOfBounds
 	}
 	oi := fv.Index(i).Interface()
 	oj := fv.Index(j).Interface()
diff --git a/model_internals.go b/model_internals.go
index e215a1f..95c0532 100644
--- a/model_internals.go
+++ b/model_internals.go
@@ -127,7 +127,7 @@ func doSave(c *mongo.Collection, isNew bool, arg interface{}) error {
 	var err error
 	m, ok := arg.(IModel)
 	if !ok {
-		return fmt.Errorf("type '%s' is not a model", nameOf(arg))
+		return fmt.Errorf(errFmtNotAModel, nameOf(arg))
 	}
 	m.setSelf(m)
 	now := time.Now()
@@ -170,7 +170,7 @@ func doDelete(m *Model, arg interface{}) error {
 	self, ok := arg.(HasID)
 
 	if !ok {
-		return fmt.Errorf("Object '%s' does not implement HasID", nameOf(arg))
+		return fmt.Errorf(errFmtNotHasID, nameOf(arg))
 	}
 	c := m.getColl()
 	_, err := c.DeleteOne(context.TODO(), bson.M{"_id": self.Id()})
diff --git a/util.go b/util.go
index 7fd5f27..eedccf6 100644
--- a/util.go
+++ b/util.go
@@ -148,17 +148,17 @@ func pull(s reflect.Value, idx int, typ reflect.Type) reflect.Value {
 
 func checkStruct(ref reflect.Value) error {
 	if ref.Kind() == reflect.Slice {
-		return fmt.Errorf("Cannot append to multiple documents!")
+		return ErrAppendMultipleDocuments
 	}
 	if ref.Kind() != reflect.Struct {
-		return fmt.Errorf("Current object is not a struct!")
+		return ErrNotAStruct
 	}
 	return nil
 }
 
 func checkSlice(ref reflect.Value) error {
 	if ref.Kind() != reflect.Slice {
-		return fmt.Errorf("Current field is not a slice!")
+		return ErrNotASlice
 	}
 	return nil
 }