diff --git a/CHANGELOG.md b/CHANGELOG.md
index 751324ccdc..5e3455af5a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Added
+
+- Added `ContentSwitcher.add_content`
+
 ## [0.67.1] - 2024-06-12
 
 ### Changed
diff --git a/src/textual/_partition.py b/src/textual/_partition.py
index be93fbe1be..09920bf579 100644
--- a/src/textual/_partition.py
+++ b/src/textual/_partition.py
@@ -21,7 +21,7 @@ def partition(
     """
 
     result: tuple[list[T], list[T]] = ([], [])
-    appends = (result[0].append, result[1].append)
+    appends = (result[1].append, result[0].append)
     for value in iterable:
-        appends[1 if predicate(value) else 0](value)
+        appends[not predicate(value)](value)
     return result
diff --git a/src/textual/widgets/_content_switcher.py b/src/textual/widgets/_content_switcher.py
index 8e63e7a502..7077232233 100644
--- a/src/textual/widgets/_content_switcher.py
+++ b/src/textual/widgets/_content_switcher.py
@@ -4,6 +4,7 @@
 
 from typing import Optional
 
+from ..await_complete import AwaitComplete
 from ..containers import Container
 from ..css.query import NoMatches
 from ..events import Mount
@@ -98,3 +99,34 @@ def watch_current(self, old: str | None, new: str | None) -> None:
                     pass
             if new:
                 self.get_child_by_id(new).display = True
+
+    def add_content(
+        self, widget: Widget, *, id: str | None = None, set_current: bool = False
+    ) -> AwaitComplete:
+        """Add new content to the `ContentSwitcher`.
+
+        Args:
+            widget: A Widget to add.
+            id: ID for the widget, or `None` if the widget already has an ID.
+            set_current: Set the new widget as current (which will cause it to display).
+
+        Returns:
+            An awaitable to wait for the new content to be mounted.
+        """
+        if id is not None and widget.id != id:
+            widget.id = id
+
+        if not widget.id:
+            raise ValueError(
+                "Widget must have an ID (or set id parameter when calling add_content)"
+            )
+
+        async def _add_content() -> None:
+            """Add new widget and potentially change the current widget."""
+            widget.display = False
+            with self.app.batch_update():
+                await self.mount(widget)
+                if set_current:
+                    self.current = widget.id
+
+        return AwaitComplete(_add_content())
diff --git a/tests/test_content_switcher.py b/tests/test_content_switcher.py
index a5e329e497..cc1e37a3e9 100644
--- a/tests/test_content_switcher.py
+++ b/tests/test_content_switcher.py
@@ -107,3 +107,16 @@ async def test_set_current_to_unknown_id() -> None:
         )
         with pytest.raises(NoMatches):
             pilot.app.query_one(ContentSwitcher).current = "does-not-exist"
+
+
+async def test_add_content() -> None:
+    async with SwitcherApp().run_test() as pilot:
+        switcher = pilot.app.query_one(ContentSwitcher)
+        await switcher.add_content(Widget(id="foo"))
+        assert not switcher.query_one("#foo").display
+        await switcher.add_content(Widget(), id="bar", set_current=True)
+        assert not switcher.query_one("#foo").display
+        assert switcher.query_one("#bar").display
+        assert switcher.current == "bar"
+        with pytest.raises(ValueError):
+            switcher.add_content(Widget())