So vs Thus

When to use each in English, with meaning, register, and examples.

So

High-frequency chunk A1 adverb

Thus

Formal Top 2,000 (common) B2 adverb

Most formal: Thus Most common: So

	So	Thus
Pronunciation	🇬🇧 /["/səʊ/"]/ 🇺🇸 /["/səʊ/"]/	🇬🇧 /["/ðʌs/"]/ 🇺🇸 /["/ðʌs/"]/
Meaning	used to say that something is true or to show a result	for this reason; therefore
Example	She was tired, so she went to bed early.	Many scholars have argued thus.
Register	Neutral	Formal
How common	High-frequency chunk	Top 2,000 (common)
CEFR level	A1	B2
Part of speech	adverb	adverb
Collocations	so happy, so much, so good, so far, so fast	thus it follows, thus far, thus far into, thus we conclude
Antonyms	not	therefore, consequently
Common mistakes	Confused with 'very' — 'so' indicates a result rather than degree., 'So' used incorrectly at the beginning of formal sentences., Overusing 'so' in formal writing, making the text less precise.	Using 'thus' in casual conversations where 'so' is more appropriate., Confusing 'thus' with 'that' in terms of meaning., Using 'thus' incorrectly as a conjunction instead of an adverb.
Usage notes	Used to connect sentences, showing cause and effect. In informal contexts, it can start statements or express agreement but may be considered vague in formal writing.	Used primarily in writing or formal speech. It can sound too stiff or old-fashioned in casual conversation. Avoid using it in everyday chat.

See it in real clips

The Lord Of The Rings › The return of the king

Thus have I walked.

Thus

Frequently asked questions: So vs Thus

What's the difference between So and Thus?

So: used to say that something is true or to show a result Thus: for this reason; therefore

Which is more formal: So and Thus?

Thus is the most formal of these.

Which is more common: So and Thus?

So is the most common in everyday English.

Which is more advanced: So and Thus?

Thus is the highest level, at B2, on the CEFR scale.

Are So and Thus the same CEFR level?

So: A1, Thus: B2 on the CEFR scale.

What part of speech are So and Thus?

So: adverb, Thus: adverb.

Can you show an example of each?

So: She was tired, so she went to bed early. Thus: Many scholars have argued thus.

Can I use So and Thus interchangeably?

Not always. So and Thus are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.