Why are the days of sefiras haomer counted at the beginning but the weeks at the end?

Question

When counting sefiras haomer, we count the number of the day we are about to start but the number of the week we have most recently completed. For example, on the first day we say "today is one day" even though we have not yet completed the first day as it is just starting. On the other hand, when we count weeks, we don't count a week until we reach the end (e.g. "today is seven days which are one week"). What is the reason for this inconsistency?

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EDIT

To address the questions that have come up in the comments and answers so far, there are a number of ways the days and weeks could be counted consistently. For example, "Today is day 1, which is one day of the first week of the omer." Alternatively, as Double AA mentioned in comments, simply counting days and weeks separately: ״היום יום אחד לעומר. השבוע שבוע אחד לעומר״

Answer 1

I think the answer is closely related to understanding the answer to Why do we count Sefirah cardinally rather than ordinally?. In other words, we count the number of days that have passed since the beginning of the counting.

So, @AlBerko is on the right track here. The Judaic day begins at nightfall. Once that day has begun, we have to count, correct? We're not really looking at how much of that day has passed. We're just interested in the fact that a new day has begun, therefore, that's one more day to add to the count.

I would say to apply the same logic to the weeks. We're looking at how many weeks have passed since we started counting (i.e., cardinally). We're not looking at which week we are in. So, we wouldn't say on Day 1, "Today is 1 day, and we're in the first week." That doesn't match up with the time that has passed and been actually counted. Therefore, on Day 7, when truly a full week of days has actually been passed and counted, we say at that point, "today is 7 days which is 1 week."

Answer 2

I think we count the weeks the way we do since it's just less cumbersome being that we don't count the weeks as a total without details.

That is, we don't call the entire first week 'week one' and the entire second week 'week two'. As opposed to let's say years, when you (or the Torah) say a two year old cow, that leaves the question open, are we discussing a cow that finished two years since birth, or is it in it's second year. But either one is acceptable as far as language used.

Our count of weeks includes the fraction of the weeks, which gives a more accurate total. That is, the days besides the total weeks.

So imagine day eight: Today is day eight which is one week and one day as we do it, vs today is day eight which is two weeks less six days.

Answer 3

Maadanei Yom Tov says that we are counting days since the day commemorating Yetzi'as Mitzrayim. So that "hayom yom echad ba'omer" means one day elapsed since that moment in time, not that it is the first day. We are indeed counting "at the end" of one day, as you put it. Here is his argument:

Why is it that we celebrate Shuvu'os on the 6th of Sivan, and call it Zeman Matan Toraseinu -- the time of the giving of our Torah, when the Torah was actually given on the 7th?

Also, why is the Torah ambiguous about how many days to count? Quoting Vayiqra 23:15-16:

וּסְפַרְתֶּ֤ם לָכֶם֙ מִמָּחֳרַ֣ת הַשַּׁבָּ֔ת מִיּוֹם֙ הֲבִ֣יאֲכֶ֔ם אֶת־עֹ֖מֶר הַתְּנוּפָ֑ה שֶׁ֥בַע שַׁבָּת֖וֹת תְּמִימֹ֥ת תִּהְיֶֽינָה׃ עַ֣ד מִֽמָּחֳרַ֤ת הַשַּׁבָּת֙ הַשְּׁבִיעִ֔ת תִּסְפְּר֖וּ חֲמִשִּׁ֣ים י֑וֹם וְהִקְרַבְתֶּ֛ם מִנְחָ֥ה חֲדָשָׁ֖ה לַה׃

And from the day on which you bring the sheaf of elevation offering — the day after the day of rest — you shall count off seven weeks; they must be complete. You must count until the day after the seventh week — fifty days; then you shall bring an offering of new grain to Hashem.

Are we counting 7 weeks = 49 days, or 50 days? And while one might be tempted to say that Shavuos "the day after the seventh week" is the 50th day, what the verse actually says is to count 50 days until the day after the seventh week -- the weeks we were just talking about when we said 49. Not including it.

The answer is that we're counting from day 0. For us today, day 0 is the first day of Pesach. On the second day of Pesach we say "This is one day in/toward the omer" -- it's a day since day 0. And we would be bringing the qorban omer to mark the completion of 1 day, thus we count the time completed.

However, on the original Pesach, day 0 didn't begin at nightfall. The actual Exodus was during the day. And since (as per the quoted verse) omer has to count complete days and weeks, that meant their day 0 was on the second day of Pesach. They counted 49 days from that time, and thereby reached the 7th, not the 6th of Sivan.

So, we count a duration of 49 days, but because there is a 0th day, the last day of our count is a 50th day. Thus, both verses are fulfilled.

But, that means we are counting days from a t=0, and thus days too are "counted at the end" of the day.

Answer 4

The verses say: Vayikra 23:15-16:

And from the day on which you bring the sheaf of elevation offering—the day after the shabbath—you shall count off seven weeks. They must be complete:

you must count until the day after the seventh week—fifty days; then you shall bring an offering of new grain to Hashem.

Finally we have a verse in Devarim 16:9

You shall count off seven weeks; start to count the seven weeks when the sickle is first put to the standing grain.

If 7 weeks is a כלל and 50 days is a פרט, then we have a sequence of כלל-פרט-כלל, which according to the rules of Rabbi Yishmael must give priority to the פרט i.e. to counting days:

כְּלָל וּפְרָט וּכְלָל אִי אַתָּה דָן אֶלָּא כְּעֵין הַפְּ֒רָט.

6. A rule followed by a detail, which is in turn followed by a rule, may infer only what is similar to the detail.

Now the last כְּלָל is from Devarim, which is considered Derabannan for some opinions (r. Yishmael against r. Akiva). Therefore, we still count weeks after counting days.

This explains why, if one counted days but not weeks, according to Mishna Berura 489:1 S"K 7 (some opinions) bediavad one fulfills the obligation, but it's better to repeat without a bracha. That's because counting of days is more important. However if one counted weeks but not days - according to all opinions one did not fulfill the obligation. As clearly, counting of the weeks is less important.