How to enable the sidebar in finder?

Solution 1:

Carefully move the pointer to the left side of the finder window border till the cursor changes to arrow pointing to the right.

Hold and Drag to the right.

If that did not work you need to restore the finders preferences.

In terminal run

rm ~/Library/Preferences/com.apple.sidebarlists.plist

and

rm ~/Library/Preferences/com.apple.finder.plist 

Restart.

Solution 2:

For me, the solution is that I need first (by Apple mis-logic) to hit:

"View / Show Toolbar" (T);

…then "View / Show Sidebar" (S) becomes ungreyed.