So

The tricky points of English  

Meanings and use of the word  so 

It's a fact of language that sometimes it is the shortest smallest words that cause the greatest problems for learners. Perhaps that's not surprising. Many words are short, because they are common; like is, or be or to or so. As essential common words, they've evolved for centuries, and their shortness has helped them to survive. They may not always be easy to use, but they are easy to remember. Many short words have several different meanings, sometimes very different meanings. "So" is a very good example of this.

The different meanings of so

The word So has five common uses in English.  Very simply, we could express these by describing the five different functions in a few words

• So expresses consequence, with the general meaning of therefore
• So expresses purpose, with the meaning of in order that
• So expresses addition, with the general meaning of and also
• So expresses a degree; it is an intensifier with a meaning similar to very
• So expresses agreement or confirmation, with a general meaning of "it is true" or "it is the case".

Now, let's look more closely at each of these,.

So expressing consequence.

  In this case so is a conjunctive adverb expressing a consequence.  This is the fundamental meaning of so as a connector. The subordinate clause of consequence mustfollow the main clause. In example A1, you might imagine that there could be an ambiguity between consequence and purpose; but this is not ambiguous for English-speakers. A soclause following a main clause must imply consequence unless it refers to future time. (Compare with example B1 below).

Examples A:

1. I took my umbrella with me, so I didn't get wet.
   (To express purpose with the same words, we would need to invert the clauses:  So I didn't get wet, I took my umbrella. This can only imply purpose.)
2. It was raining, so we stayed at home
3. The pilots are all on strike, so there are no flights today
4. They both have good jobs, so they have plenty of money.

So expressing purpose

In this case, so is a subordinating conjunction, expressing a purpose. It can either be used alone, or else in the expression so that. The subordinate clause of purpose can either preceed or follow the main clause.
So that is usually preferred if the subordinate clause of purpose comes before the main clause. 

• To express purpose, so that is more commonly used than just so by itself (essentially to avoid ambiguity between purpose and consequence):
• so, by itself, is mostly used to introduce clauses of purpose when they refer to future time, or relative future time (examples B1 and B5), as in these cases the meaning of socannot be ambiguous. It must mean purpose, not consequence. Compare examples A1 (consequence) and B1 (purpose) .

So as is used to express purpose, particularly in spoken English. In this case the verb in the secondary clause is in the infinitive with to (example B6).

Examples B:

1. I took my umbrella with me, so I wouldn't get wet.
   (We can also say: So I wouldn't get wet, I took my umbrella)
2. So that you understand this, I'm making it as clear as possible.
3. So you understand me, I'm being as clear as possible.
4. I'm being as clear as possible, so you understand me.
5. I took the fast train, so I'd get home early.
6. I'm taking the small roads so as to avoid the traffic on the motorway.

Note: So or in order for expressing purpose?

 As a general rule, so that is much more common than in order that (except in formal written language), and to or in order to are generally preferable to so as to (except in informal spoken language). See Styles of English.

So expressing addition

In this case, so is again a conjunctive adverb. It expresses an additional or a duplicate action. In this case, so introduces the second clause (unless there is a conjunction), and the verb and the subject of this clause are inverted.

Examples C:

1.  I once lived in Bombay, so did my boss.
2. He says he's got the answer, but so does everyone else.
3. This computer has broken down, and so has that one.

So expressing a degree

So does not quite mean the same as very; it is an intensifier, an adverb of degree qualifying an adjective, and  expressing relative high degree, or a perception of high degree. 
It is often used to qualify an adjective in a statement of consequence.
Unlike other intensifiers (very, quite, etc) so it not usually used with attributive adjectives (adjectives that preceed the noun), but only with predicative adjectives. These children are so good is acceptable; these so good children would not normally be considered as acceptable, even if so is sometimes used in this way. It is more normal to say These are such good children. See ► Uses of such.

Examples D:

1. This ice-cream is so good.  (meaning extremely good in my opinion)
2. This ice-cream is ever so good.
3. The computer is so old that it breaks down twice a week.
4. This computer is so old; let's get a new one.
5. You'd work better if you didn't talk so much.
6. I'd buy more of these, if they weren't so expensive.

So expressing agreement or confirmation

So can have the meaning of "that" or "it is true" or "that that is true". 
In this sense it a substitute word, a pro-form but not really a pronoun, as it refers back to a whole statement, not to a noun. (To refer back to a noun, we would use the pronoun it orthey).  It confirms - often strongly - a statement that has already been made, or in some cases implied. It can be used in dialogue to confirm the answer to a question.

Examples E:

1. He was very angry, and he told me so.
2. I'm going to London next week, or at least I hope so.
3. You shouldn't really stop work before six, but you can do so today.
4. "Do we have enough money?"  /  "I think so"
5. "Will they ever know what really happened ?" / "I don't think so."
6. "You told the judge that you had forgotten?"  / "That is so."
7. "You were in London last night, weren't you?" / "Quite so."
8. So you've finished at last, have you?

Some other functions of so

So is used in a number of idiomatic phrases, such as "so and so", "and so on" or "so-so" . Here are some examples with explanations.

Examples F:

1. So and so said you were coming. (meaning an unspecified person).
2. ...... and so on.  (meaning... and more of the same)
3. I'm feeling so-so today. (meaning not too bad, not too good).
4. So! That's the answer. (The initial free-standing so expresses surprise or another emotion)..

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