What form is “öfters” that it requires an “s” (sentence shared in post)

Question

In this sentence, why does “öfters” have the “s”? I believe the verb is in Konjunktive II, but why is the word “öfter” being modified?

“Wenn ich mehr Zeit hätte, ginge ich öfters spazieren.”

Answer 1

In your example you can choose öfter or öfters as you please.

There is the difference, that öfter is a comparative as you correctly observed. So in most cases it asks for something else to be compared to, as opposed to öfters which can happily appear without comparison (meaning somwhat frequently). Since your sentence has the comparison situation (you don't have more time) both are correct.

Note, that comparatives can appear on their own with a different meaning. This question concerns that construction, called absolute comparative.

Answer 2

I fully agree with the existing answer (guidot) on the semantics of öfters vs. öfter: öfter can be used in comparisons ("öfter als..."), or as a standalone adverb ("somewhat frequently"); öfters only has the second usage.

I would like to add something specifically on the ending -s, since this is actually the core of your question: "Why is öfter being modified?". This is originally a genitive ending.

David Vogt suggests that the -s is simply the "adverbial suffix that occurs in many other words as well: anders, stets, links, besonders, eigens". That is, a suffix that creates an adverb from a word that can only be used as an adjective (ander-, ... eigen-).

However, this doesn't apply to öfters, since öfter is already an adverb that can cover the same semantic ground. Therefore, I disagree with reading the -s as an adverbial suffix.

Instead, it has its roots in the genitive declension, which is commonly marked by -s. I quote (and adapt) from the DWB:

öfters, Adv. Seit dem 17. Jahrh. wird der Genitiv des Komparativs öfter als Adv. gebraucht neben und statt öfter [...]; durch Ellipse entstanden aus öfters Mals (s. DWb oftermals bei oftmal 2, b).

In other words, öfters was the genitive of [a comparative adjective] öfter, commonly used in the expression öfters Mals, i.e. "on rather frequent occasion". (A more modern option: öfter mal.)

The existence of the synonymous expression des Öfteren also underpins this explanation of öfters. By surface analysis, des Öfteren is clearly a genitive form of the nominalized adjective öfter. I believe that des Weiteren and weiters display the same pattern.

Finally, note that there still is a usage of öfter- as an (attributive) adjective, besides its chief function as adverb (seine öfteren Besuche, bei öfterer Verwendung...), which Duden characterizes as "umgangssprachlich".

Answer 3

As has been pointed out, öfter and öfters are synonyms. They can be used to express a comparison (although many speakers seem to prefer öfter for this use).

Passiert das jetzt öfters als früher? (Tagesspiegel, 31.3.2001)*
Does this happen more frequently now than before?

They can also be used to express a certain frequency of something (absoluter Komparativ in German; compare English an older gentleman): öfter, öfters "from time to time, every now and then, on occasion; repeatedly, frequently, many times".

Das ist eine Erfahrung, die ich schon öfters gemacht hatte.
That's an experience I've had many times before.

The -s is an adverbial suffix that occurs in many other words as well: anders, stets, links, besonders, eigens.

* ^{Some further examples from newspapers found by searching for öfters als in DWDS corpora:}

^{Entsprechend komme es öfters als früher vor, dass Betroffene fest vereinbarte Termine versäumten […]
Man denkt viel öfters als sonst vor einem Spiel an mögliche Situationen […]
Auf Fotos sah man ihn nun öfters als früher entspannt lächeln […]
Leider verfehlt er den Korb aber auch öfters als früher bei den Chicago Bulls.
Am Mittwochabend und am Donnerstagvormittag klingelte beim Trainer von Hertha BSC das Handy noch öfters als gewöhnlich.
Der Gläubige muß öfters als bisher wiederkommen und das Lichtlein entzünden.
Auch die Berufstätigen gönnen sich öfters als andere eine Ferientour.
Mehrmals wurden sie vorübergehend festgenommen – sie öfters als er.
Und öfters als man glaubt ist es ein dunkler Winkel in einem Keller der Peripherie, wo das junge Glück beginnt, wo eine Familie begründet wird.}