Theory and Experiments
This is not enough as, some experiments are1:
For these reasons simulation is proposed at the third pillar of science. Some disagree with this statement, but regardless, computer simulations are very important in modern science, be they as a pillar of their own or as an essential part of theory and experiment.
More generally called Computational X to work for all disciplines
Computational X covers the broad range of challenges
Developing the tools to allow others to make progress