Can Pages be put in Categories?

No – only posts can be filed under categories.

OK, thanks. Here is what I am trying to do with Categories:

I use Widget Logic to control which sidebars appear on which pages. I would like the same sidebars to appear a specific parent page and all its subpages. If I could make categories it would be easy, without that it appears to be a very difficult task with Widget Logic.

Use the is_page() conditional?

The only way I have found to do that is to use is_page(array()), then list all the subpages under the parent. This is cumbersome as these subpages change occasionally

does the Widget Logic plugin support custom taxonomies? I believe you can assign those to pages, to function like categories

You can do it using the links widget instead of the categories widget. You could create link categories and then place links to the pages you want in those categories, then place the links widget in your sidebar.

You could create link categories and then place links to the pages you want in those categories, then place the links widget in your sidebar.

That would control which pages appear on the sidebar. The OP is trying to control which sidebar appears on certain pages