Of all the roles in football, the concept of the holding midfielder may have caused the most debate over the Premier League's first 25 seasons.
Traditionally, English football eschewed the holding midfielder entirely, in favour of two box-to-box players who dovetailed in defensive and attacking duties. Then the holding player became an accepted concept, with David Batty in the mid-1990s and Claude Makelele in the mid-2000s underlining the importance of that role in different ways. Next, deep-lying playmakers were briefly popular.
Now, there's a broader range of styles, and Chelsea's meeting with Liverpool on Friday night will offer a particularly interesting contrast in this respect.