"If practicable" was, if not expressed, understood. If the Army commander is standing behind your left shoulder and says, "I want that hill," there is no discretion allowed -- he knows the situation.
If, however, he is a mile or so away and says, "I want that hill," you may assume that he's expressing a tactical desire and that he might well be unaware that there's four batteries and three brigades up there. If he really, really wants that hill, he'd say, "Take that hill at all hazards."
Obviously, Lee wanted Cemetery Hill and perhaps Culp's Hill, but not so desperately as to order Ewell to effuse excessive blood.
Lee gave Ewell the discretion -- kinda gentlemanly, wouldn't you say? I doubt that Ewell could have taken the hill when the "wish" was issued. So then we have to figure how badly Lee wanted the hill(s). Perhaps he hadn't yet assayed its (thier) importance?
Another great book to read is Scott Bowden and Bill Ward's book "Last Chance for victory" which analyzes the if practable debate in depth...I highly recommend it. I have to get ready for work so I can't articulate their thesis but rest asured it is impressive and thought provoking to say the least...
I have read the Bowden and Ward book several times. I would highly recommend it.
Their thesis is that Lee gave the order to Ewell to attack Cemetary Hill on the first day of Gettysburg with the ending "if practicable" as a matter of courtesy. The staff officers who transmitted the message, Ewell's subordinate officers and Ewell's troops understood that they were to attack the Hill and said so in their after action reports. Only Ewell interpreted the orders to mean "if I could do so to advantage" as he stated in his report. Even on its face Ewell's argument is weak in that he did not know if he could take the Hill "if he could do so to advantage" unless he tried. The fact is he didn't try until it was too late.