[MENTION=38424]Alatar[/MENTION], that occurence of "concealed" in the characterisation of "total cover" came up in the recent long-running Hiding thread.
I've steered clear of that one. The WotC folk are doing too much shoulder shrugging on that issue to make it amenable to consensus. The terminology they chose to frame the issue, "lightly obscured" and "heavily obscured", and the definitions they assigned to those terms, wherein heavily obscured non-intuitively means utterly opaque and lightly obscured means who knows what, pretty much removed the possibility of clarity.
I think [MENTION=6787503]Hriston[/MENTION] was probably right when he suggested that "concealed", in that occurrence, doesn't mean literally mean "concealed from sight" but something more like "sheltered behind the cover" because "lacking a clear path". That makes the wording infelicitous - as you note - but preserves coherence.
Indeed, if you redefine "completely concealed" to mean something other than the plain meaning of the phrase, the inconsistency can be made to vanish. I would argue that requiring the reader to make such a leap is unreasonable and that ignoring the error in the text, if that's what it is, in order to hold down the errata word count, mindful of the mess they made in the previous edition, is less than laudable.
Otherwise a character behind a gelatinous cube or glasssteel or similar - who is not concealed in the literal sense - would also not enjoy protection from attacks (because, under the mooted interpretation, not enjoying cover) which seems pretty counter-intuitive.
The phrase, "enjoy protection from attacks" begs the question, what kind of attacks? A missile attack would surely run into any obstruction between the attacker and target. A disembodied skeletal hand appearing as of out of nowhere and attaching itself to the target might be another matter. The Wall of Force description states that "nothing physical can pass through the wall", very specific language. We like very specific language. It affords clarity of meaning. The Chill Touch skeletal hand does not traverse the distance between caster and target and, therefore, does not pass through the wall, or the window, as the case may be. Seems rather clean cut. But no, that clarity of meaning, that very specific wording, does not lead us to the correct answer. Rather, like the phrase "completely concealed", it's meaning needs to be twisted or discounted to fit the later ruling.
Furthermore, a creature standing at the end of a darkened hallway might be completely concealed, though there is no solid object between it and a potential observer. The decision to define total cover as being completely concealed was indeed infelicitous, so much so that whether you and I can come to an agreement on the meaning of the text is beside the point. The pages of discussion that precede these posts attest to the problem.
In other words, they screwed this particular pooch so badly that a single phrase dropped in somewhere cannot resolve it. And that is probably why we haven't seen an amendment through 5 subsequent printings.
I have no preference as to how spells with remote effects interact with walls of force. I just want it to be clear, as well it might be. In that regard, the authors have let us down and seem unwilling to rectify the problem, for reasons about which we can only speculate, as I have done herein.
