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know a hawk from a handsaw

To be able to tell two things apart. The phrase comes from Shakespeare's Hamlet. Of course I know which twin is which, I know a hawk from a handsaw, after all!
See also: hawk, know

know chalk from cheese

To be able to tell two things apart (especially by recognizing their differences). Of course I know which twin is which, I know chalk from cheese, after all! Leah has a beauty mark under her left eye, and Deena doesn't.
See also: chalk, cheese, know

know for a fact

To have definitive knowledge of something. I know for a fact that he cheats in cards! I saw the ace up his sleeve. My mom says she knows for a fact that I'm getting the internship at her company, but I won't believe it until the recruiter calls me.
See also: fact, know

know (something) inside and out

To be well-versed in and/or very familiar with something. I'm ready for this exam—I know genetics inside and out! I think Mary will do great at the audition, now that she knows the dance inside and out. These cabbies know the city streets inside and out.
See also: and, inside, know, out

know (one's) beans

To be knowledgable about and/or very familiar with something. I had no idea you were such a good piano player—you really know your beans!
See also: bean, know

know (someone)

To have a familiarity with someone; to know who someone is. Such familiarity can range from close friendship to having only met someone once. Oh yeah, I know Mr. Meyers, he used to be my neighbor. He knew Vanessa long before she became a famous singer.
See also: know

know what's o'clock

To be attentive and aware of all that is going on. Those students thought they could get away with cheating in my class, huh? Too bad I know what's o'clock!
See also: know

know which way the wind blows

To be able to anticipate how a certain course or situation is likely to develop. These politicians know which way the wind blows regarding public opinion on the issue, and you can bet they'll vote accordingly.
See also: blow, know, way, wind
References in classic literature ?
He had seen you indeed, before he came to Bath, and admired you, but without knowing it to be you.
Natasha glanced at her ironically without knowing why.
But after knowing you even for this short time, I knew you were quite the opposite of that, and I remembered that the first thing you had done on coming into the money had been to offer me half, so the information that you were the Lord Dawlish whom I had been hating did not affect me.
Nutty invites you down here, knowing that you are Lord Dawlish.
The woman that was with me had told me that by a mere accident, knowing nothing of what importance it was to me.
husband), and to tell him who I was; but not knowing what temper I might find him in, or how much out of temper rather, I might make him by such a rash visit, I resolved to write a letter to him first, to let him know who I was, and that I was come not to give him any trouble upon the old relation, which I hoped was entirely forgot, but that I applied to him as a sister to a brother, desiring his assistance in the case of that provision which our mother, at her decease, had left for my support, and which I did not doubt but he would do me justice in, especially considering that I was come thus far to look after it.
But when I thought it over a little, I felt more hopeful for your knowing at once that I had only been watchful for you, and had only noticed what I think I have noticed, because I was quickened by your interest in it.
Knowing all this,--and still always going on with infinite endurance, pains, and perseverance, could his dark soul doubt whither he went?
It might be worth knowing what this strange man's business was with Lightwood, or Wrayburn, or both, at such an unseasonable hour.
It read something like this: "An architect is someone who starts out knowing nothing about everything and as time goes on learns less and less about more and more.
There's a lot more to drama studies, comedic timing and improvisation than just putting on blond hair and playing a ditz or knowing how to cry on cue.
That would make the office atmosphere better, the work would get done, the patients would get better care, and I think everyone would feel better about what was accomplished, knowing that we did it as a team.
Camp people find comfort in knowing that throughout the whole year, no matter what goes wrong, everything will be ok once you get to camp.
As the authors come to the knowing of self, other, task and situation from various frameworks, and cross boundaries of leadership knowledge, we hope the reader enjoys the essays on teaching leaders and leadership contained herein.
If I am willing to look in that mirror and not run from what I see, I have a chance to gain self-knowledge--and knowing myself is as crucial to good teaching as knowing my students and my subject.