What is the difference between 要するに and つまり?

Question

I read that 要するに and つまり are not always interchangeable. Still, I don't really understand the difference between the two...

Answer 1

Not 100% sure on this, but I think つまり is used more for rewording something, while 要するに is more for "summing up" the "preceding" statements into a "conclusion".

Answer 2

The two can be interchangeable but where as 要するに means "To summarise" or "in short". つまり is usually taken to mean "in other words":

大敗した。要するに 力の差があった。

It was a big defeat. In short, there was big difference (in strength).

財布をなくした。つまり お金がない。

I have lost my wallet. In other words, I have no money.

There is a similar word to つまり、すなわち which also means "in other words" but is not interchangeable because it does not convey a a conclusion:

母の兄、 すなわち おじさん。| My mother's elder brother. In other words my uncle.

I explain this because (I think*) in the following sentence つまり is interchangeable with either 要するに or すなわち, illustrating the nuance you are asking about.

友人の仕事は危険で、汚くて、おまけに きついらしい。ちなみにそういう仕事は俗に「３K」と呼ばれている。要するに「き」、すなわち「K」が３つつくというわけだ。

I understand my friend's work is dangerous, dirty and hard. This kind of work, incidently is commonly referred to as 3Ks work. In short the　３ "ki"s or "K"s often come together.

*I should be grateful for if others would confirm correct me on this.