Most important/influential philosophical articles of the 20th-century?

A philosophy graduate student writes:

I've been following your blog for a couple years now, and one of the most beneficial things you've done (for me, at least) is post about the significance of certain philosophers and philosophical works. For instance:

Most Important Philosopher in the last 200 years: http://leiterreports.typepad.com/blog/2009/03/so-who-is-the-most-important-philosopher-of-the-past-200-years.html

Most Important Philosophy Books and Articles since 2000: http://leiterreports.typepad.com/blog/2009/12/what-were-the-bestmost-important-philosophy-books-and-articles-of-the-past-decaden-since-2000.html

I'd like to request another inquiry of this sort: What are the most influential philosophical articles written during the 20th century? I understand "articles" to exclude book chapters; these should be works that appeared (at least initially) in academic journals. I am quite curious what people will mention in the comments, though I suspect Gettier's "Is Justified True Belief Knowledge?", Frankfurt's "Alternate Possibilities and Moral Responsibility", and Nagel's "What Is It Like to Be a Bat?" will be among them.

I think getting answers to this question would be helpful for graduate students looking to familiarize themselves with the core articles that have shaped the literature in both their specialty areas and philosophy as a whole.

A good topic, I think; comments are open for reader input.