Former vs. Previous

Former and previous are used to describe someone or something that used to exist or occur but no longer exists or occurs; but there are subtle differences between them:

“Former” implies “of the past, having taken place in the (historical) past.”
“Previous” means only “before”—as in a sequence.

The opposite of previous is next and the opposite of former is latter. Followings are the comparisons between the two :

1- Former and previous can be used to describe someone who had a particular position, role or job in the past, but no longer has it:
 
- …former President Richard Nixon…
- He pleaded not guilty to murdering his former wife.
- The ceremony honored all the former presidents who are still living.


A former president of the USA refers to any of presidents that used to be in that position (e.g. Abraham Lincoln or George H. W. Bush).The previous president means any president just before the one under discussion.The president of the USA is only the one who was in that position before the current president of the USA. (current president of the USA is Barack Obama; George W. Bush was before him); or any president that was before any other president in that position in the past (e.g. Ronald Reagan was before George H. W. Bush).

- “When Lincoln took office, he found that the previous president had left him some unfinished business.”
- In 1798, George Washington was “the former president,” but there was no “previous president.”
- The former employee of the company had lost her three previous jobs.
2- Former is used to refer to countries which no longer exist or whose boundaries have changed:

- …the former Soviet Union.
- …the former Yugoslavia.
In this use previous is rarely used.

3- Former and previous is used to describe something which used to belong to someone or which used to be a particular thing:

- …the former/previous home of Sir Christopher Wren.
- …a former/previous monastery.
- Their farm has been reduced to half its former/previous size.
Their difference follows the one was described in No.1.

4- Former and previous is used to indicate that something comes proceeding in place or arrangement:


- The former chapter of the book refers to any of the chapters you used to read.
- The previous chapter of the book implies the chapter just before the one you are reading.

5- The two words are used to indicate that something occurred in the past:

- The former/previous correspondence.
- The former/previous world champion.

6- Former and previous both are used to describe a situation or period of time, which came before the present one. Former is more formal than previous; but previous is much more common:

- He would want you to remember him as he was in former/previous years.
- Marble pillars and high painted ceilings remain from former/ previous times.


Previous refers to the period or the thing immediately before the one that you are talking about:

- It was a surprisingly dry day after the rain of the previous week.
- She looked tired after her exertions of the previous evening.


7- When two people, things, or groups have just been mentioned, you can refer to the first of them as the former. Previous in this use is not used:

- Given the choice between a pure white T-shirt and a more expensive, dirty cream one, most people can be forgiven for choosing the former…
Opposit:latter

Resources
Mcmillan Dictionary
Collins Cobuild dictionary