David Deutsch – Explanations
David Deutsch gives a brief talk on explanations and their role in progress.
Read more on progress: http://plato.stanford.edu/entries/scientific-progress/ (Section 4. Is Science Progressive? is especially interesting).
And if you enjoy the history and philosophy of science, you should (if you haven’t already) enjoy a good dose of Kuhn: http://plato.stanford.edu/entries/thomas-kuhn/.