Particles: Subject 가 / 이 and Topic 는 / 은

Here is something very important that makes every sentence sound all the more fluent but that has been in part neglected by main textbook I have been using as the main reference for previous posts.
Some textbooks and grammar books teach topic and subject particles together... and with good reason, since depending on context they can be used interchangeably with nouns in the first sentence marked with the subject particle but subsequently being used with the topic particle. It all makes sense, in a Korean way.
For this post I am mostly referencing (or outrightly copying word by word) the information provided by the Talk To Me In Korean lesson 9 (level 1).

-가 / -이

These are the subject marking particles and used to emphasise the subject of the sentence. In English this is not used due to the way we construct sentences (and I am afraid the word construct is Portinglish, I'm aiming to revise it later). However, in Korean there is sometimes the need to mark the subject to make ensure the correct understanding of what we are trying to say.

-는 / -은

Here is something very important that makes every sentence sound all the more fluent but that has been in part neglected by the main textbook I have been using as main reference.

Some textbooks and grammar books teach topic and subject particles together... and with good reason, since depending on context they can be used interchangeably with nouns in the first sentence marked with the subject particle but subsequently being used with the topic particle. It all makes sense, in a Korean way. (Post edit: Some grammars refer to this particle as subject particle which makes things very difficult. Let's settle for the existing distinction and only be aware of the confusion.)

For this post I am mostly referencing (or outrightly copying word by word) the information provided by the Talk To Me In Korean lesson 9 (level 1).

Formula:

NOUN + 은 / 는

Attached to a noun or phrase to emphasise what is being talked about or which part of the sentence our attention should really be focused on. The closest to topic marking particles that we can find in English is the addition of "as for..." before a noun.

Example
- 오늘 오후에 시간 있어요? Are you free this afternoon?
- 오늘 오후에는 시간 옶어요. Not this afternoon.
The emphasis in in afternoon giving the impression that meeting up is not a problem at some point in time, just not this particular afternoon. The introductory dialogue in this chapter provides more examples that make use of the topic particle to show the subtlety if its use in Korean.

My own makeshift example using soju, more specifically "The man drinks soju."

남자 소줌셔요. The man drinks soju.

남자가 소주 마셔요. - The man (is the one that) drinks soju.

This is a tricky one since we could have easily used the topic particle instead of the subject particle since in this sentence. In this sentence "the man" is both the subject and the topic. In some cases, after using the subject particle in the first or introductory sentence, the speaker then shifts to using the topic particle. In English we don't use this, however the logic is the same as when we refer to the subject as "John" in a first sentence but from then on use the personal pronoun "he".

남자는 소주 마셔요. - (As for) the man (he) drinks soju.

It is the man, definitely the man, there is no doubt that the man, not the woman next to him, let alone the child, it is he who drinks soju. Instead of emphasising "the man" as the subject of the sentence, "the man" is emphasised as the topic of the sentence.

남자가 소주는 마셔요. - The man drinks soju.

Here the subject particle is in "the man", so he is the one we are talking about as being the subject for the action (the action is determined by the verb). Additionally, the topic particle is in 'soju' perhaps because the speaker wants to emphasise that the man is drinking soju and not some other drink. The man, our subject and hero, could be drinking 먹골리 but NO! he is drinking soju and this is the fact that we want to emphasise since perhaps it is unusual to see someone drinking soju at that place and somehow that seems to be an important thing to emphasise. Soju! Definitely soju!

The use of topic and subject becomes easier to understand in comparative sentences where something is emphasised in comparison to something else.

SHINee is good but BIGBANG은 is simply amazing!

As for me은 I like BigBang. Dzenan은, on the other hand is more of an multi company boy.