systematic和systematical有什么区别？

像systematic和systematical的区别？还有一些其他类似的比如，electric/electrical; clinic/clinical; scientific/scientifical等。有什么好的区分方式？

There is no one-size-fit-all rule which distinguishes a word ending with “-ic” with “-ical”.

It all depends on the words in question.

The discussions below are over-generalized for demonstration purposes only and you can actually argue differently in many cases.

1.      systematic (adjective) vs. systematical (adjective)
“Systematic” is completely synonymous with “systematical”.
If you really want to split hair, actually many dictionaries do not include “systematical” as a defined word. Therefore “systematic” is a more commonly used word than. “systematical”.

2.      electric (adjective) vs. electrical (adjective)

a.       “Electric” refers to things which run on electricity, e.g., electric car, electric wire.

“Electrical” refers to things relating to electricity, e.g., electrical engineer, electrical component.

b.      “Electric” can be used metaphorically, e.g., Tempo of the game was electric. But you cannot say “tempo of the game was electrical”.

3.      clinic (noun) vs. clinical (adjective)
“Clinic” is a noun referring to health facility or group.

“Clinical” is an adjective referring to medical treatments/observations. It can also be used to describe someone who is unemotional.

4.      scientific (adjective) vs. scientifical (??)
There is no such word as “scientifical”.