General or specific keywords for content network?

which will give more impressions?

[redstar08]

Does adding more specific keywords to an otherwise general adwords raise or lower the number of impressions?

For example, if I have "cats" and then add "kittens" to the same ad group, have I expanded my reach by allowing the ads to show up on pages that have "cats" or "kittens" or have I limited my reach by showing up only on pages that have the words "cats" AND "kittens"?

[Rehan]

The content network doesn't use keywords in the same way as the search network. Instead of matching to specific keywords, pages are shown based on the theme of the active keywords in the ad group. As it says at [adwords.google.com...] :

To determine whether to place your ad on a content page, the AdWords system considers the theme of all the ads and keywords in the ad group. For this reason, it's important that each of your ad groups is built around a consistent theme. Focus on only one of the products or services that you're advertising. This helps ensure that your ads appear on the most relevant content pages.

The rest of that page is useful reading, too.