Page 564 - Practical English Usage 3ed - Michael Swan, Oxford

2 Itoldyouso
I told you so usually means 'I warned you, but you wouldn't listen to me'. Mummy, I've broken my train. - I told you so. You shouldn't have tried to
ride on it.
3 other verbs
So cannot be used after all verbs of saying. We cannot say, for example, She premised me 86.
541 sohaveI,soamIetc
1 so + auxiliary + subject
We can use so to mean 'also', before auxiliary verb + subject. The structure is used to answer or add to what came before. Note the word order.
Louise can dance beautifully, and so can her sister.
I've lost their address. - So have I.
The same structure is possible with non-auxiliary be and have.
I was tired, and so were the others.
I have a headache. - So have I.
After a clause with no auxiliary verb, we use do/does/did.
He just wants the best for his country. - So did Hitler.
We do not normally use a more complete verb phrase in this structure. We can say, for example, So can her sister, but not 86 etln .'le,. sister' ilanee.
2 so + subject + auxiliary
So can also be followed by subject + auxiliary verb (note the word order) to express surprised agreement.
It's raining. - Why, so it is!
You've just put the teapot in the fridge. -So I have!
For neitherlnor am I etc, see 374.
542 so much and so many 1 the difference
The difference between so much and so many is the same as between much and many (see 357). So much is used with singular (uncountable) nouns; so many is used with plurals.
I had never seen so much food in my life.
She had so many children that she didn't know what to do. (NOT ••• S6 mtteh
, "ltl ... ev"'~1t
We use so, not so much, to modify adjectives and adverbs (see 538.5,6). You're so beautifuL (NOT l'tUt're S6 mtteh beal1tijrtl.)
But so much is used before comparatives (see 140). She's so much more beautiful now.
sohaveI,soamIetc 541
page 532