Function of "too" in the phrase "so too" or "so, too,"

Question

I just ran into this sentence in an online article:

But as the App Store’s fortunes rose, so too did the iPhone’s, and later the iPad’s.

If I were editing that sentence, I would remove the too on the theory that it doesn't add anything to the sentence's meaning beyond what so provides. On the other hand, the phrase "so too" (or "so, too,") is quite common in everyday speech and writing, and it may be idiomatic for some speakers and writers. Site searches for "so too" and "so, too," reveal that these terms appear a total of 25 times on EL&U pages—mostly in answers, and mostly by extremely well-informed answerers.

If we think of so in the quoted example as meaning "in a like manner" and too as meaning "in addition," it seems to me that the sense of too is embedded in the sense of so, since Event B can't happen in a like manner to Event A unless it is happening in addition to Event A. But perhaps I'm overthinking this and the main point of too is simply to emphasize the also-ness of Event B.

Here's my question: Is the too after so in sentences like the one quoted above superfluous to the sense of the sentence, or does it contribute a shade of meaning that I may not be recognizing?

Answer 1

You phrased it well in your question:

the main point of too is simply to emphasize the also-ness of Event B.

In the immediate context of your example, the App Store is important because it strengthens the market appeal of the iPhone and the iPad. ‘Event B’ — hardware sales — is the star of the show.

The title of another relatively recent online article illustrates this well:

This land is your land... and so, too, is the ocean.

The ‘so, too’ here means something like ‘you already know that this is the case for land [from the Woody Guthrie song], but I want to talk specifically about the ocean.’

Answer 2

So is part of the so X/such a(n) X that S construction. It's a quantifier, in the sense that it measures the degree of some predication. And it's a pro-form -- that is, it stands for something else, like a pronoun does for a noun -- and in the case of

... as the App Store’s fortunes rose, so too did the iPhone’s ...

it stands for what happened to the iPhone. The App Store's fortunes rose, and so did the fortunes of the iPhone. I.e, the constituent above "comes from"

• ... as the App Store’s fortunes rose, so too did the iPhone’s fortunes rise

by a sort of So-tag formation that

• pivots the clause around the so fulcrum,
• inverts the subject NP with a dummy Do-support auxiliary
• reduces the subject,
  by deleting (the repeated) material in iPhone's (fortunes rose).

Quite a complicated construction, with a lot of specialized syntax.
Note that one clause uses rose but the tag has to use did ... rise;
and the deleted material has to be totally identical to the material in the first clause.

This requires simultaneous parsing and pattern matching at oral speeds,
which is a bitch to program, and which is buggy in rapid speech and writing.

Answer 3

The 'too' in 'so too' means also. Hence 'so also...'. It is a legitimate, even eloquent phrase, providing that it is not overused.