diff --git a/inc/activities/create.php b/inc/activities/create.php
new file mode 100644
index 0000000..f44893a
--- /dev/null
+++ b/inc/activities/create.php
@@ -0,0 +1,50 @@
+<?php
+namespace activities\create;
+
+/*
+Create a new post or comment (depending on $activity["object"]["type"]),
+copying $activity["actor"] to the object's "attributedTo" and
+copying any recipients of the activity that aren't on the object
+to the object and vice-versa.
+*/
+function handle( $actor, $activity ) {
+    if ( !(array_key_exists( "type", $activity ) && $activity["type"] === "Create") ) {
+        return new WP_Error(
+            'invalid_activity', __( 'Expecting a Create activity', 'activitypub' )
+        );
+    }
+    if ( !array_key_exists( "object", $activity ) ) {
+        return new WP_Error(
+            'invalid_object', __( 'Expecting an object', 'activitypub' )
+        );
+    }
+    if ( !array_key_exists( "actor", $activity ) ) {
+        // TODO validate that $activity["actor"] is the URL of the $actor
+        return new WP_Error(
+            'invalid_actor', __( 'Expecting a valid actor', 'activitypub' )
+        );
+    }
+    $object = $activity["object"];
+    $actor_id = $activity["actor"];
+    $object["attributedTo"] = $actor_id;
+
+}
+
+
+function reconcile_receivers( $object, $activity ) {
+    // TODO copy "audience", "to" "bto", "cc", "bcc"
+    // to both object and activity from each other
+}
+
+function copy_field_value( $field, $from, &$to ) {
+    if ( array_key_exists( $field, $from ) ) {
+        if ( array_key_exists ( $field, $to ) ) {
+            $to[$field] = array_unique(
+                array_merge( $from[$field], $to[$field] )
+            );
+        } else {
+            $to[$field] = $from[$field];
+        }
+    }
+}
+?>
diff --git a/inc/outbox.php b/inc/outbox.php
index e8f6119..a03f34f 100644
--- a/inc/outbox.php
+++ b/inc/outbox.php
@@ -46,7 +46,9 @@ function persist_activity( $actor, $activity ) {
 function handle_activity( $actor, $activity ) {
     if ( !array_key_exists( "type", $activity ) ) {
         return new WP_Error(
-            'invalid_activity', 'Invalid activity', array( 'status' => 400 )
+            'invalid_activity',
+            __( 'Invalid activity', 'activitypub' ),
+            array( 'status' => 400 )
         );
     }
     switch ( $activity["type"] ) {
@@ -68,6 +70,9 @@ function handle_activity( $actor, $activity ) {
         break;
     case "Undo":
         break;
+    default:
+        // handle wrapping object in Create activity
+        break;
     }
 }
 ?>