I've been doing some research and I came across the idioms "not to know A from B" and "not to know a B from a bull's foot". As far as I know they seem to have the same meaning "to be ignorant" or "to know nothing". But I believe that somehow the 2nd one is more emphatic than the 1st one, but this is just my personal feeling. I'd like to know what do you think about this. Are they the same?
Learn English – “not to know A from B” VS “not to know a B from a bull’s foot”
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Related Solutions
Redundancy for emphasis
You are correct that adding "on foot" is redundant, since "walk" already implies that. However, saying "walk on foot" is still grammatical. "On foot" functions as an adverb modifying "walk". It's redundant, but it adds emphasis. A person might say "walk on foot" in a situation where they wanted to emphasize the fact that you're not driving, or perhaps that a person's sore leg would give them pain.
Many common English constructions use redundancy for emphasis or extra clarity. Here are a couple more examples:
Let's walk on up the hill.
You could just say "Let's walk up the hill." The "on" just adds some extra emphasis, also suggesting that you are continuing your current walk. Consecutive prepositions often work this way.
It may be possible to find you a direct flight to Manchester.
"May" means "possibly", so technically that's redundant. One could also say, "Possibly you could find a direct flight to Manchester." Using two constructions in the same sentence that both mean "possibly" adds emphasis, either suggesting that the possibility is unlikely or expressing optimism by emphasizing the possibility.
If you'd like to read more about this, look up "pleonasm". Something like it probably happens in your native language, too.
Extended meanings
There's another reason why someone might say "walk on foot": you might have just been using the word "walk" in an extended sense. For example, you might just have been talking about riding in an Imperial Walker from Star Wars:
or referring to this old slogan from U.S. telephone companies, encouraging customers to look up a phone number in the phone book and call ahead before visiting a business:
or any of thousands of other possibilities.
Dictionary definitions can't possibly explain all the meanings that people can give a word. But people usually understand the difference between a primary meaning and an extended meaning. Redundancy can often help discourage a listener from understanding a word in an extended meaning in a situation where the extended meaning might seem relevant.
Picture sources: starwars.com, Cazbah.
To make do is a verb form that is composed of two verbs such as to make believe which means:
To pretend or imagine.
The past form of to make do with is made do with. You have to use the past form of to make as it is the first verb and an object of the verb to make is implied in the context.
Best Answer
Short answer: They are the same.
"not to know a B from a bull's foot" might be used in some rural places, or some non-USA places, but I've never heard of it. Other similar phrases (besides the "his ass from his elbow" mentioned above are "he doesn't know his ass from a hole in the ground" and "he doesn't know shit from Shinola". Shinola is or was a brand of shoe polish.
I don't think there is really any difference in the meaning of these. It's really a difference in where they can be said. I suspect that somebody wanted to say "shit from Shinola" in a place where that would be a dirty word, so he changed it to "A from B" to clean it up. Even if that's not what really happened, I would prefer using these in this order:
That is, I will use the highest one on the list that is compatible with the place I'm at and people I'm with. I can't imagine myself using "A from B"--If I were someplace where I couldn't say one of the other ones, I wouldn't say anything like that. The point of this sort of phrasing is in the humor. In fact, if there is any difference at all in them, "A from B" might be stronger, because the person saying it is insisting on calling this guy dumb without a bit of humor lightening it up.
Ignore the fact that in real life it is easier to distinguish one's ass from one's elbow than it is to distinguish one's ass from a hole in the ground. And it's harder than both of those to distinguish shit from Shinola.