SouthofGrey wrote on 02/10/17 at 17:52:48:
I want to be able to play the opening based on understanding of the position rather than having to memorize a bunch of "only moves" or concrete sequences to get out of the opening.
The Scheveningen is a great opening, where you won't have to memorize long sequences of "only" moves. It's also not an opening where the defense rests on a hairline. One of the nice things about the Scheveningen is that, in the main lines, Black doesn't move the pawns in front of his King. This makes the King's position more resilient and forgiving. One mistake won't necessarily sink you; it often takes a couple of Black mistakes for White to crash through. Compared to something like the Dragon, where even the tyros know to pry open the h-file and sac, sac, mate, White has to work harder in the Scheveningen to drum up an effective attack.
However, the Scheveningen is also not an opening that can be played on general understanding; at least not well. The Scheveningen is complex, with a lot of different plans and pawn breaks. This flexibility is the Schevy's greatest strength and its greatest weakness. It is difficult to understand. For both sides.
For example, in the Classical Scheveningen lines where White plays Be2, Black has to be on the look out for White to attack with (i) e4-e5, (ii) f4-f5, or (iii) g4-g5. What do you do as Black when one of these happens? These types of decisions cannot be made solely based on general considerations; they take calculation and a feel for the position that comes from having studied Schevy games and theory.
There are countless other decisions that Black has to make in the Schevy. What do you do with your little center? Do you keep the pawns intact or do you play for ..e5 or ..d5 and, if so, when. Again, these decisions are hard to make, and they take calculation and study. As a friend of used to say, "Don't just move by hand, remember your ABCs -- always be calculating."
Martin C. gives good advice. If you want to start in on the Scheveningen, play the modern lines where you omit ..a6. These are easier to learn, cut down on the choices, and can be a stepping stone to the classical lines, when you are ready. I would recommend the repertoire that Soltis himself gave in a Chess Digest pamphlet on the Schevy. (See the next post.)