Quirrell models himself as more intelligent than Harry, and has had far more time to plan, so he expects to win in any even contest. Being able to lie grants both parties great flexibility of options, which he expects to make better use of than Harry.
However, Quirrell seems to dislike lies—half truth, yes, misleading information, yes, but blatant lie is just not in his style. Whether this is an inherent feature of his character or sense of honour, or he wants to keep open the possibility to confirm his words later in Parseltongue if need be, that’s an open question.
The lips twitched again, and then went flat. “Then I shall skip it. Mr. Potter, you sometimes make a game of lying with truths, playing with words to conceal your meanings in plain sight. I, too, have been known to find that amusing. But if I so much as tell you what I hope we shall do this day, Mr. Potter, you will lie about it. You will lie straight out, without hesitation, without wordplay or hints, to anyone who asks about it, be they foe or closest friend. You will lie to Malfoy, to Granger, and to McGonagall. You will speak, always and without hesitation, in exactly the fashion you would speak if you knew nothing, with no concern for your honor. That also is how it must be.”
There was silence, then, for a time.
That was a price measured in a fraction of Harry’s soul.
Because EY wants the chapter to be not-annoying to read, might be one good reason.
Quirrell models himself as more intelligent than Harry, and has had far more time to plan, so he expects to win in any even contest. Being able to lie grants both parties great flexibility of options, which he expects to make better use of than Harry.
However, Quirrell seems to dislike lies—half truth, yes, misleading information, yes, but blatant lie is just not in his style. Whether this is an inherent feature of his character or sense of honour, or he wants to keep open the possibility to confirm his words later in Parseltongue if need be, that’s an open question.
Inherent feature. We’re told this in chapter 51: