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As displayed in this answer by nixda one can nicely compare how often do certain words appear in "lots of books", in lots of languages. When reading the answer it's plausible to want to do some cross checks. For instance, the obvious failure of this tool (and of course, I don't think google would be worried about a pair of persons believing it or not) would be not to detect changes concerning the Reform der deutschen Rechtschreibung von 1996.

So one compares dass vs. daß, and as expected, at 1996 the plots from Ngram show the sudden sharp dropping of daß and the sharp rising dass (the derivative of the curves —or rather the derivatives of the smoothed version of this curves— at 1996 are sharply jumping, is almost discontinuous). But there is something interesting there too, besides the 1996 critic point.

Just as it happens in 1996, it sounds to me plausible to associate discontinuities of the derivative to some "external force" on the language —say new orthography rules, a word becoming taboo, and so on. One can therefore expect to obtain from violent changes in the graph, certain information about the language, which might have some sociological background as well. And this might be wrong, of course; it's just a toy model.

The point being that, when one plots the frequency of dass and daß one obtains that

  • dass was broadly used in the second half of the XIX Century.
  • dass fluctuates at 1945.

enter image description here

Here one could think that it's just as it is, and it should be accepted. But consider now the pair (muss, muß). Actually the plot is easier to read if we ignore all other words, i.e. just consider how often muss was used out of the words (muss, muß). The result is strikingly similar to the dass,daß-case. In fact, both plots are quite the same:

enter image description here

  1. Does somebody know if there are phenomena associated to this changes?
  2. Did the "German Orthographic Conference of 1901" change ss into ß exactly opposite to that of 1996?
  3. What happened at 1945? WWII effects? (e.g. absence of data, not enough books?)
  4. What is the "miracle" behind the striking similarity of the dass and muss curves?

A more recent question pointed out the occurrence of the similar peak about 1945. There gerne and gern are contrasted.

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3 Answers

up vote 9 down vote accepted

First, of all, it looks as if Google digitalised the long s (ſ) as s most of the time.

Then, one has to consider the following four variants of s-spelling. I distinguish between the case where a long s (ſ) is used (mostly blackletter fonts) and where it is not (mostly antiqua fonts):

  1. Heyse’s rules – ſs (ss) after short vowels:
    dass, müsst, ließ (antiqua);
    daſs, müſst, ließ (blackletter)
  2. »modified Heyse« – ſs (ss) after short vowels, ſſt instead of ſst:
    dass, müsst, ließ (antiqua);
    daſs, müſſt, ließ (blackletter)
  3. Adelung’s rules – ß also after short vowels:
    daß, müßt, ließ (antiqua and blackletter)
  4. No ß at all (Switzerland and fallback solution, if ß is unavailable):
    dass, müsst, liess (antiqua);
    no blackletter equivalent (as far as I know)

Since muss and dass are affected equally by all four rule sets, whoever spells dass will almost certainly spell muss and not muß. This mostly answers question 4. In addition, muss and dass are almost certainly the two most common words in which the four variants differ. Therefore they are less affected by statistical fluctuation and most writers were confident about the spelling of those words. For rarer words like Fluss and Kuss, the similarity is less prominent. The similarity is also smaller for words, for which variant 1 and 2 differ. Since they should not differ, if ſ were always digitalised as s, I assume that ſs was digitalised as ß sometimes.

A good way to find out, what is going on, is to separate the case, starting with variant 4, since it can be extracted most easily by looking at words like Straße that are written with ß in all other variants. As can be seen from this Ngram, variant 4 accounts almost perfectly for the remaining dass spellings between 1910 and 1996. I would explain its detailled temporal evolution as follows:

  • From 1901 to ca. 1925, variant 4 is strongly decreasing. This is probably due to the antiqua ß becoming widely available (it was only »invented« in the 19th century), thus reducing the need for the fallback solution ss. Another factor might be people who refused to use the ß altogether (at least in Antiqua) and only started to do so as the official rules became widely accepted (see below).
  • After this, variant 4 is gaining popularity again slowly until ca. 1940, which is most probably due to the ß getting out of use in Switzerland.
  • There is a strong peak for variant 4 in 1945, which might be due to World War II, which can be assumed to reduce the text output by the fighting countries. Since Switzerland did not participate in the war, its output can however be assumed to be rather constant at the same time, which would raise the relative impact of Swiss books and thus of variant 4, explaining the peak. Afterwards, the book output of the rest of the German speaking world rose again, thus reducing the relative impact of Swiss books and variant 4 to normal. (This assumption is also backed by this Ngram, if you assume that Swiss books use words referring to Switzerland more often.)
  • Afterwards the fraction of books that uses variant 4 remains mainly constant, since Switzerland had almost fully abolished the ß by then, while elsewhere, the antiqua ß as well as the orthography from 1901 were sufficiently established, such that almost nobody needed to use the fallback solution anymore.

Now, let’s look at the remaining time:

Before 1901, things were complicated. There were no generally accepted official spelling rules, however certain governments or parts of them issued spelling rules, e.g., certain schools in Austria were directed to use Heyse’s rules in 1879. As can be seen from this Ngram, it looks as if variant 4 was becoming increasingly popular – however this might also be due to antiqua fonts becoming more popular and people not using the ß in these fonts, e.g., due to uncertainty about spelling, lack of the glyph, etc.¹ However, when subtracting the ratio of people who presumably used no ß at all, we obtain an estimate of the fraction of users who used variant 1 or 2. Only between ca. 1890 and ca. 1910 this estimate seems to be more than just statistical fluctuation, and then it is about 5 %, while variant 3 is used by about 35 %. So, when variant 3 (Adelung) was established as part of the new official spelling rules in 1901, it can be estimated that it was already used by the majority of those who used the ß at all. The sharp drop of dass and muss at that time must thus be attributed to other factors, e.g., people starting to use the ß at all in certain fonts¹.

Finally, the orthography reform of 1996 reintroduced Heyse’s rules, which explains the sharp increase of dass and muss after that year.

¹ Note that the ß originated from blackletter fonts and existed in those for a long time. It can therefore be safely assumed, that blackletter fonts without ß were not an issue – moreover since most blackletter text printed worldwide at that time was German.

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We have a similar feature and we'd like @Wrzlprmft to weigh in. german.stackexchange.com/questions/10355/… –  philshem Feb 11 at 9:50
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I can only speculate about the questions 1-3, but I think that I can answer you last question concerning the "miracle" of the almost identical curves. If I am getting this right, Google Books is scanning all its books for these words and the plots show the ratio of their occurrence.

Now if grammar allows two different forms - in this case ss and ß - , an author or publisher who wants to write a book will first decide for one form and then stick with it for both dass/daß and muss/muß throughout the entire book. So if he decides to switch from dass to daß in his next book, he will also choose muß instead of muss. It's just a matter of consistency.

If we look at the problem this way, the second diagram doesn't show how often dass and muss appeared in books at a special time, but how many authors chose the ss-form instead of ß in their books at that time.

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Some background regarding Ngram viewer: 5.2 mio books until 2008, they count+analyse all words per year, Y-axis in percent shows how many of them are the searched word, the amount of released books has a direct influence into that percentage. See Why do I see more spikes and plateaus in early years? (scroll down) –  nixda Oct 23 '13 at 21:58
Well, that makes lot of sense. (However when one plots ass VS aß on top of that, one sees no such an effect. But this is perhaps, because is not so common word (wrt. daß, muß).) –  c.p. Oct 24 '13 at 5:53
@c.p.: That’s most probably, because is written like that according to all ß rules (except the Swiss ones), since the ß is preceded by a long vowel. –  Wrzlprmft Oct 24 '13 at 13:36
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The obvious similarity in the frequency of spelling ss or ß at the end of a word can be nailed down to the reforms of the orthography which took place in 1901 (II. Orthographische Konferenz), and in 1996 (Reform der deutschen Rechtschreibung).

In the conference in 1901 it was decided to spell according to Adelung (i.e. spelling the sharp 's' at the end of a word as 'ß'). Before that we also had the spelling according to Heyse (i.e. spelling as 'ss' at then end). This officially replaced the Adelung-rules in 1996.

Note that in Switzerland we do not have an ß at all. Hence all documents having a Swiss origin will not show this difference.

These reforms will not explain the peak occuring in 1945 to the end of World War II. We can only guess that many documents archived from Google from these post-war days may not have been written on a German typewriter with access to the letter 'ß' (same peak also occurs for e.g. Straße vs. Strasse).

See also: What caused "ss" to gain popularity over "ß" in the 19th century?

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gerne/gern shows a similar peak in the late 1940s. Would you be willing to weigh in to our discussion: german.stackexchange.com/questions/10355/… –  philshem Feb 11 at 9:51
@philshem: I did read your interesting question there... first thing I did was to turn off smoothing too. Second thing was to look how many sources and which books were used for generating these numbers... sadly not too many. Hence I believe it's a statistically not significant coincidence we have here but hard to knock this opinion down to facts. The answer you already have is pretty close to what I expected to get. It may even be a single editor preferring gerne over gern who may have produced this peak. –  Takkat Feb 11 at 10:06
Thanks for checking into it. (btw Grüezi NachbarIn). edit, I'm writing an article and I use gern/gerne as an example, hence the digging. –  philshem Feb 11 at 10:12
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