Positional and Tactical Understanding

The Mechanics' Institute Chess Room Newsletter #406 is out, always a high point of the day! IMJD quotes from Michael Aigner http://fpawn.blogspot.com : Three-time US Champion Grandmaster Nick DeFirmian, rated 2541 FIDE, taught the most recent session of the San Francisco School of Chess on July 12-13...Over two days, GM DeFirmian shared a number of opening concepts with the students of the School of Chess.He taught the top group (five students and two guests) for nearly four hours on Saturday, advocating a positional approach to understanding the move orders and strategies to play the 6.Be3 line of the Najdorf Sicilian... It was interesting to watch how even an ultra-tactical opening such as the Najdorf could be understood by a calm positional approach.

Is chess understanding tactical or positional? Or is it a combination of both?