Let’s review the relationship one more time between slide masters and themes. A theme is a set of formatting specs. Themes are not applied directly to slides—they are applied to slide masters, which are then in turn applied to slides. The slide masters exist within the presentation file itself. You can change them by applying different themes, but they are essentially “built in” to the presentation file.
When you change to a different theme for all of the slides in the presentation, your slide master changes its appearance. You can tweak that appearance in Slide Master view. As long as all of the slides in the presentation use the same theme, you need only one slide master. However, if you apply a different theme to some of your slides, you need another master, because a master can have only one theme applied to it at a time. PowerPoint automatically creates the additional master(s) for you, and they are all available for editing in Slide Master view.
If you later reapply a single theme to all of the slides in the presentation, you do not need multiple masters anymore, so the unused one is automatically deleted. In addition to all this automatic creation and deletion of slide masters, you can also manually create and delete slide masters on your own. Any slide masters that you create manually are automatically preserved, even if they aren’t always in use. You must manually delete them if you don’t want them anymore.
In the following sections, you learn how ...