In a question referring to the statement
The average age at which people die of heart diseases is decreasing.
The answer says that using reducing is preferable to using decreasing.
How does one decide between using reducing and decreasing, as both are similar in meaning?
I just came across a fine line between the two words, and I hope it works. It seems that in 'reducing', an external force is used.
When we say
He has been _______ the intake of sugar since he was diagnosed with diabetes.
(reducing / decreasing) --> I would use "reduced" because it is something done by him.
while
The number of students, appearing for this paper, is __________.
(reducing / decreasing)--> I would use "decreasing" as it's something not done by anyone.
In addition to the active/passive nature of the terms pointed out in the other answer, the words are also distinguished in terms of whether they describe a reduction in quality or quantity. If something is decreasing, it is getting smaller in a quantitative sense. If something is reducing, it can also be diminishing in a qualitative sense.
One could say "he was reduced to a shell of a man" or "the city was reduced to rubble", both of which describe a qualitative change. You cannot "decrease" a city to rubble, because there is no quantitative change - there is still one city, but its character has been diminished. "Reduce" can also be used in a quantitative sense, however, so it may be a bit more versatile than "decrease".
