Where did this unusual phrase come from? How can you know something "across and along"? At first glance, the phrase really sounds rather strange, but it is still possible to explain its meaning.
What they want to say by this
Most often, the expression is used when a person says that he has studied some locality in all the subtleties and details. We see a vivid example of the use of this phrase with A. S. Pushkin: “I know a side,” answered the road, “thank God, it’s traveled far and wide.” This means that he knows the whole district well, he traveled all over on his tarantass and is well oriented here.
If you try to understand more deeply what “up and down” means, it is best to parse each word separately. So, the word “along” means “in length, on the long side”. In turn, “across” means “in width,” or “on the short side.” Of course, it is difficult to imagine that a person studying the area will go back and forth in straight lines, then where did this phrase come from?
If you imagine this phrase in the form of an image, you can see how in the old days weavers weaved canvases, laying longitudinal and transverse threads. The interweaving of these threads was very strong, they fit snugly together. Perhaps this phrase was born from here? How closely the threads lie in the fabric, the terrain is so thoroughly studied.
In relation to people
Sometimes they say about people that they know them “across and along”. Undoubtedly, the study of the anatomical structure of the human body is not meant here, although doctors may well say so. In everyday life, most likely, this phrase is used as a symbol of the fact that we know a person very well and have long been familiar with him. Here we can give an analogy with the saying "eat a pound of salt" with someone. That is, to be with a person for a long time and study it well.
This can be said about each other by close people, relatives or colleagues who have worked together for many years. As a rule, over many years of living together or working, people find themselves in many situations that help them in the intricacies of knowing the nature of a relative or colleague, his personal qualities and form a stable opinion about this person. Then we can safely say that "I know Ivan Ivanovich Ivanov across and along."
Other use cases
In the dictionaries there are other meanings of this phrase. For example, there is a short prayer that a woman read while escorting her husband on a long journey: “God save the husband far and wide, and I will never go beyond him.”
When the master gives the task to the workers, he can say that they study the instructions across and along - that is, in great detail and scrupulously. This emphasizes the importance of work.
It is sometimes used as an expression of a contradiction in something: "it looks along, but lives across." That is, he says one thing, but does the other, does the opposite. Or when a person disagrees with someone’s opinion.
The same phrase is used when something is very skewed or something needs to be found in the room, when something is studied in detail or a sheet of paper is written tightly in different directions. As a rule, this happens if there is no more paper, and you need to make notes.
We conclude
How to distinguish "along" and "across"? When it comes, for example, to folding a sheet of paper first in length and then in width, or about folding a piece of fabric, the sides are distinguished according to these parameters. In our case, the phrase does not apply to mechanical concepts, so we will not separate the words. It is enough to understand that it means “good to know, study, understand” a place, person, phenomenon or object. Or comprehensively study a topic or problem.
In old dictionaries, this phrase is spelled a little differently: "both up and down." However, the meaning is still the same.
And constantly people strive to ensure that this is how to know everything - in full detail.