Article and no article

I don't understand why preceding the first and second "society" there is no article "a", but for the third one the article "a" has been put there.
When should use article "a" when not?

Context:
That politicians wield power, sometimes enormous power, cannot be disputed, but regard politics as the decisive influences in setting society's long-term direction betrays a misunderstanding of what makes human beings tick. Society may be ultimately governed by a power that not even the strongest government can control very long: the mind and the imagination of a society's intellectuals and artists.