<Brag about> vs <Boast about>

Question

According to the dictionary definition the two words "boast about someone / something" and brag about someone / something" are so close in meaning that I cannot differentiate between them. Are they interchangeable? If not, what would you interpret or how do you use each one?

Please have a look on the explanations below:

Brag

To speak too proudly about what you have done or what you own:

Example: She's always bragging about how much money she earns.

Boast

To speak too proudly or happily about what you have done or what you own:

Example: Parents enjoy boasting about their children's achievements.

For instance, do the sentences below mean the same thing:

1. Her son has written four articles and published them in many popular scientific journals. She always boasts about her son.
2. Her son has written four articles and published them in many popular scientific journals. She always brags about her son.

Or

3. He is a very wealthy man. He always boasts about the money he earns.
4. He is a very wealthy man. He always brags about the money he earns.

Please help me to find out any possible nuance.

Answer 1

Both words are equally old, yet boast seems to me very slightly better in a formal context than an informal one, and brag very slightly better in an informal than a formal one.

The only reason I can think of for this is that, when being scornful (in the school playground for example) it is easier to say, "He's bragging" with a sneer, than it is to say, "He's boasting" with one. You can drag bragging out to fit a good long sneer: "He's brr-AGG-ing". The first vowel sound in Boasting doesn't lend itself to sneering. So maybe as children we used and heard brag more than boast, and perhaps - from childhood on - we think of boast as more "teacherish": more formal.

However, do remember that this is a very slight nuance. In your examples the words really are interchangeable.