Мне наплевать на последствия.
vs: Мне наплевать на следствия.
On the surface, they both seem to mean "consequence", the sense presumably originating from the word "след/track/footprint".
I wonder why in this specific instance, "последствие" with the prefix "по-" is the one to go for? Why does the use of "следствие" sound odd here?
Следствие often (though not always) has neutral meaning as in 'cause - effect' pair (причина - следствие), while последствия(-е) is typically about something negative, like delayed bad results from some event/action (событие/действие - последствия).
Следствие (singular) is widely used in the math in the meaning of effect / consequence, like in a logical pair cause - effect, and also in the meaning of investigation (criminal).
The word следствия is either a plural form or genitive of следствие.
The word последствие has a very close (if not the same) meaning result / effect / aftermath / consequence. But in some circumstances it has a negative connotation. For instance:
Последствия пожара
Последствия болезни
Also it makes sense to mention a preposition вследствие which has a meaning as a consequence of.
следствия is a plural form of the word следствие. Isn't it?
следствие as "criminal investigation" does not have a plural form.
Commented
Mar 21, 2018 at 10:09
Последствие is a thing or event that starts/happens at some point in time.
Я [не] думаю|беспокоюсь о последствиях - I [don't] think|care about what can happen [because of it].
Курение приводит к негативным последствиям: одышке и т.д. - Smoking has negative consequences like wheeze etc.
Дождь вызвал последствия в виде наводнения - Rain caused the flood.
Следствие (in sense of effect, not investigation) is an abstract thing, which is true since its cause is true. Synonyms are вывод, заключение.
Теорема имеет следующие следствия (not последствия) - From the theorem you can draw the following corollaries.
Следствия, которые мы можем вывести из этих фактов, таковы... - From the facts we can conclude that ...
But in some set phrases (Следствием ... является ...) it is used instead of последствие.
Следствием дождя явилось наводнение. - The flood came as a consequence of the rain.
Следствием курения являются заболевания легких - Lung diseases are caused by smoking.
You can use последствие here as well and it will sound only a little unusual.
