diff --git a/src/plottools/common.py b/src/plottools/common.py
index 9a6a736..5217e17 100644
--- a/src/plottools/common.py
+++ b/src/plottools/common.py
@@ -27,7 +27,7 @@
 import matplotlib.ticker as ticker
 
 
-def common_xlabels(fig, axes=None):
+def common_xlabels(fig, *axes):
     """ Reduce common xlabels.
 
     Remove all xlabels except for one that is centered at the bottommost axes.
@@ -36,14 +36,16 @@ def common_xlabels(fig, axes=None):
     ----------
     fig: matplotlib figure
         The figure containing the axes.
-    axes: None or sequence of matplotlib axes
+    axes: Sequence of matplotlib axes
         Axes whose xlabels should be merged.
-        If None take all axes of the figure.
+        If not specified, take all axes of the figure.
     """
-    if axes is None:
+    if len(axes) == 0:
         axes = fig.get_axes()
-    if isinstance(axes, np.ndarray):
-        axes = axes.ravel()
+    if len(axes) == 0:
+        return
+    if len(axes) == 1 and isinstance(axes[0], np.ndarray):
+        axes = axes[0].ravel()
     coords = np.array([ax.get_position().get_points().ravel() for ax in axes])
     minx = np.min(coords[:,0])
     maxx = np.max(coords[:,2])
@@ -68,7 +70,7 @@ def common_xlabels(fig, axes=None):
             done = True
 
 
-def common_ylabels(fig, axes=None):
+def common_ylabels(fig, *axes):
     """ Reduce common ylabels.
 
     Remove all ylabels except for one that is centered at the leftmost axes.
@@ -79,12 +81,14 @@ def common_ylabels(fig, axes=None):
         The figure containing the axes.
     axes: None or sequence of matplotlib axes
         Axes whose ylabels should be merged.
-        If None take all axes of the figure.
+        If not specified, take all axes of the figure.
     """
-    if axes is None:
+    if len(axes) == 0:
         axes = fig.get_axes()
-    if isinstance(axes, np.ndarray):
-        axes = axes.ravel()
+    if len(axes) == 0:
+        return
+    if len(axes) == 1 and isinstance(axes[0], np.ndarray):
+        axes = axes[0].ravel()
     coords = np.array([ax.get_position().get_points().ravel() for ax in axes])
     # center common ylabel:
     minx = np.min(coords[:,0])
@@ -108,7 +112,7 @@ def common_ylabels(fig, axes=None):
             done = True
 
 
-def common_xticks(fig, axes=None):
+def common_xticks(fig, *axes):
     """ Reduce common xtick labels and xlabels.
     
     Keep xtick labels only at the lowest axes and center the common xlabel.
@@ -119,12 +123,14 @@ def common_xticks(fig, axes=None):
         The figure containing the axes.
     axes: None or sequence of matplotlib axes
         Axes whose xticks should be combined.
-        If None take all axes of the figure.
+        If not specified, take all axes of the figure.
     """
-    if axes is None:
+    if len(axes) == 0:
         axes = fig.get_axes()
-    if isinstance(axes, np.ndarray):
-        axes = axes.ravel()
+    if len(axes) == 0:
+        return
+    if len(axes) == 1 and isinstance(axes[0], np.ndarray):
+        axes = axes[0].ravel()
     coords = np.array([ax.get_position().get_points().ravel() for ax in axes])
     minx = np.min(coords[:,0])
     maxx = np.max(coords[:,2])
@@ -150,7 +156,7 @@ def common_xticks(fig, axes=None):
             done = True
 
 
-def common_yticks(fig, axes=None):
+def common_yticks(fig, *axes):
     """ Reduce common ytick labels and ylabels.
     
     Keep ytick labels only at the leftmost axes and center the common ylabel.
@@ -161,12 +167,14 @@ def common_yticks(fig, axes=None):
         The figure containing the axes.
     axes: None or sequence of matplotlib axes
         Axes whose yticks should be combined.
-        If None take all axes of the figure.
+        If not specified, take all axes of the figure.
     """
-    if axes is None:
+    if len(axes) == 0:
         axes = fig.get_axes()
-    if isinstance(axes, np.ndarray):
-        axes = axes.ravel()
+    if len(axes) == 0:
+        return
+    if len(axes) == 1 and isinstance(axes[0], np.ndarray):
+        axes = axes[0].ravel()
     coords = np.array([ax.get_position().get_points().ravel() for ax in axes])
     minx = np.min(coords[:,0])
     maxx = np.max(coords[:,2])
@@ -190,7 +198,7 @@ def common_yticks(fig, axes=None):
             done = True
 
 
-def common_xspines(fig, axes=None):
+def common_xspines(fig, *axes):
     """ Reduce common x-spines, xtick labels, and xlabels.
     
     Keep spine and xtick labels only at the lowest axes and center the common xlabel.
@@ -201,12 +209,14 @@ def common_xspines(fig, axes=None):
         The figure containing the axes.
     axes: None or sequence of matplotlib axes
         Axes whose xticks should be combined.
-        If None take all axes of the figure.
+        If not specified, take all axes of the figure.
     """
-    if axes is None:
+    if len(axes) == 0:
         axes = fig.get_axes()
-    if isinstance(axes, np.ndarray):
-        axes = axes.ravel()
+    if len(axes) == 0:
+        return
+    if len(axes) == 1 and isinstance(axes[0], np.ndarray):
+        axes = axes[0].ravel()
     coords = np.array([ax.get_position().get_points().ravel() for ax in axes])
     minx = np.min(coords[:,0])
     maxx = np.max(coords[:,2])
@@ -233,7 +243,7 @@ def common_xspines(fig, axes=None):
             done = True
 
 
-def common_yspines(fig, axes=None):
+def common_yspines(fig, *axes):
     """ Reduce common y-spines, ytick labels, and ylabels.
     
     Keep spine and ytick labels only at the lowest axes and center the common ylabel.
@@ -244,12 +254,14 @@ def common_yspines(fig, axes=None):
         The figure containing the axes.
     axes: None or sequence of matplotlib axes
         Axes whose yticks should be combined.
-        If None take all axes of the figure.
+        If not specified, take all axes of the figure.
     """
-    if axes is None:
+    if len(axes) == 0:
         axes = fig.get_axes()
-    if isinstance(axes, np.ndarray):
-        axes = axes.ravel()
+    if len(axes) == 0:
+        return
+    if len(axes) == 1 and isinstance(axes[0], np.ndarray):
+        axes = axes[0].ravel()
     coords = np.array([ax.get_position().get_points().ravel() for ax in axes])
     minx = np.min(coords[:,0])
     maxx = np.max(coords[:,2])