Let's start by clarifying that it's not a locution. But it still occurs to me that someone might come to a dictionary to clear up their doubts. Which evidently do not come from the motto at the top of the page but from the entry provided by Cesar Orozco. The first thing that surprises me is that he says that he is an English teacher, because a doubt like this is typical of a programming class; Whoever interprets it correctly has a good chance of passing the course. And it's been so many years since they've been resurrecting it here that I decided to do my brief and humble work. . . No, my extensive and pedantic contribution. Let's start by separating two concepts: "every 3 [something]" is not the same as "every third [something]". The first case is counted with numerals , and the second with ordinals . In numbers, the beginning is counted from 0 ( zero ) and we take it for granted that there is a sequence; In order it is counted from the first of the elements and by definition we know that there is a sequence . I mean that in a collection the first element is the one numbered 0; the second as 1; the third as 2 . . . And then, taking the original example, "every third day" from a Monday you count "Monday, Tuesday, Wednesday", and in "every 3 days" you start from the first shot of the medicine as 0 (because you can't count anything backwards) and "1=Tuesday, 2=Wednesday, 3=Thursday". Of course this would be if we use logic and not tradition or custom, because someone may have been taught differently and will end up taking their medication any day, that's why the "every other day" (or "day in between", as they call it in each place) was invented, which leaves no doubt: it is "one day, Yes; another, no." For longer periods, it is customary to use the hours since 12; 24; 48; 72 hours leave no doubt and we understand that the first shot is moment 0.
To make it easier to understand, we just have to take this logic : 1 . If on a WEDNESDAY at 6 pm you take medicine and they tell you that you must take it every 1st day. . . When do you take the next q ? Well, Thursday at 6 pm. 2 . But if they tell you to take it every 2nd. day. . . When do you take the next q ? Well, Friday at 6 pm3. And if they tell you to take it every 3rd. day, when do you take the next one? Saturday at 6 pm???????
Anonymous, with all due respect, although I understand your logic of starting time at zero, we don't use that logic when we're practical in everyday life. If I'm going to give someone three seconds to drop something, I start counting from 1, not zero. When you tell him you'll see him soon you say: "In 1 minute I'll be with you." When you ask someone to give you a little more timeout you say, "Give me 1 second". In this way being practical we always start with 1 and calculate the smallest part of time as 1, never as 0 . 0 is nothing, so we can't count it pragmatically. If we say "every third day", we do not start counting the day on which we are as 0 but as 1 and in the common and practical use, we do not ignore it to the point of not telling it.
I'm English teacher and a student, and I, we will encounter this problem. The issue of the use of this rare er concept, the common criterion is the following: what must be is made until the third day. I.e., if they now prescribe you a medication, you take it today and reopen it to take on the third day. Today Monday prescribe it to you and return it to you to take on Wednesday. They really are after 48 hours but they are three days, Monday, Tuesday, Wednesday. Wednesday restarts the count and that day as the first account, now would be Wednesday, Thursday and Friday. Monday Yes, Tuesday, Wednesday if Thursday, Friday Yes. I know that it is a concept wrong logic, but someone (we don't know who) decided to popularize the phrase of "a day and a day not", therein of "every other day". It is important to understand what refers the person who tells you because while you could be taking you a drug 3 times a week you end up tomandotelo two by the concept of every 72 hours. I recommend that you investigate the person to which you are referring, only here I explain what most people understand by "every other day".
