“Since then” vs “After that”

Since then vs. After that
“Since then” is used with the present perfect tense to talk about something that started in the past and is still going on. 

For example:

I learned about his art in high school, and since then I have loved Picasso.

Their parents died, and since then the children have lived with their uncle, Olaf.

I failed a test in my freshman year because I didn’t study, but since then I have always prepared for exams.

In all of the above sentences, the action in the second clause is still going on.  I still love Picasso, and the kids still live with Olaf, and I still prepare for exams.

 

“After that” is used to talk about things that started and ended in the past.  Even if the action was done over a period of time in the past, use “after that” if it is finished. 

For example:

I was embarrassed by my low score, and after that I studied hard. (meaning: I no longer study hard, perhaps because I am no longer a student)

Their parents died, and after that they lived with their uncle. (meaning: they no longer live with their uncle, perhaps because they are now adults).

I failed my first midterm exam, but after that I prepared for important tests. (meaning: I no longer prepare for exams)

Alternatives – “Ever Since” and “From then on”
You can also use “ever since” to talk about actions that are still going on, but it looks better at the end of a sentence:

I moved to the countryside in 2010, and have enjoyed hiking ever since.

I taught my son to be respectful, and he has been polite ever since.

You can also use “from then on” to talk about actions that started in the past, but have concluded:

I got my first bike when I was a child, and from then on I enjoyed rides around town. (meaning: I no longer enjoy rides around town, perhaps because I have left the town)

Susan got a dishwasher when she moved into her new apartment, and from then on she had a lot more free time. (meaning: she no longer has more free time, perhaps because she is dead)

Robert failed his first test, but from then on he studied diligently. (meaning: he no longer studies for tests, perhaps because he is no longer a student)

I suppose the above is somewhat “borderline.”  I suspect if you use “from then on” to talk about something still going on, 90% of readers won’t notice a problem.

 

Conclusion
I see these phrases mixed up in a ton of essays every week.  This is because student are often asked to write about examples from when they were students.