Particles are probably one of the most confusing elements in the Vietnamese language. Just by simply adding a particle to a sentence can significantly change the implication or tone of a sentence.
The “thì” emphasizes the subject which means that the clause that comes after the “thì” really only applies to whatever that came before the “thì.”
Ex. 1 Hậu duệ mặt trời với tỉ suất người xem vượt quá sức tưởng tượng đến 40% phần công lớn cũng là nhờ Song Joong Ki và Song Hye Kyo.
<em>Ratings for The Decendants of the Sun surpassed anyone’s wildest imaginations with a viewership of 40% thanks in large part due to Song Joon Ki and Song Hye Kyo. </em>
Với một người gần đây ít xem phim Hàn Quốc như tôi thì hậu duệ mặt trời đúng là một bộ phim quý hiếm.
<em>And as</em> <em>for a person like me who watches few Korean dramas these days, decendants of the sun is a rare movie</em>
<em> </em>Here the “thì” serves two functions. The first is that it marks the topic. Anything that comes before the “thì” is the topic. In this example the topic is với một người gần đây ít xem phim Hàn Quốc như tôi (For a person like me who watches few Korean dramas). Anything that comes after the “thì” is in reference to the topic, and only the topic.
The second function is that it serves as a contrast to the previous statement. The first sentence was about the fact that viewership was incredibly high for this particular K-drama. And the second sentence shows contrast by the author stating that he watches few dramas.
The sentence with the “thì” reads more like: <em>And as</em> <em>for a person like me who watches few Korean dramas these days, Descendants of the Sun is a rare drama. </em>Or you can also read it like: “<em>For a person like me [don’t know about anyone else/I can’t speak for anyone else] who watches few Korean dramas these days, Descendants of the Sun is a rare drama. </em>
<em> </em>Ex. 2 Ghi vào sổ sách nhé... tôi đã không chết vào ngày Sol 6. Đương nhiên những người còn lại trong phi hành đoàn thì nghĩ rằng tôi đã đi đời và tôi không thể trách họ.
<em>Let’s write this in the book…I did not die on Sol 6. Of course, the remainder of the crew [specifically/don’t know about anyone else] think I died and I cannot blame them.</em>
The topic here is những người còn lại trong phi hành đoàn which comes before the “thì” and nghĩ rằng tôi đã đi đời và tôi không thể trách họ which comes after the “thì” is in reference to the topic.
Also, the first sentence was a statement that speaker did not die. Second sentence shows contract by saying that the rest of the crew thinks he died.
Native Vietnamese speakers, any additions, corrections, comments?
I would use "thì" when I want to compare or contrast two (or more) things. Without "thì", the meaning of the sentence does not change.
Example 1: Tôi rất thích quyển sách này nhưng em gái tôi thì không.
Example 2: People say it all the time, when they talk about the weather: "Chuồn chuồn bay thấp thì mưa, bay cao thì nắng, bay vừa thì râm."
In your first example, we could just replace "thì" by a comma. The word "thì" makes the sentence "smooth" to read.
Your second example illustrates my point above. Sự thật là tôi không chết. Mọi người thì nghĩ rằng tôi đã chết. - We're contrasting the fact and what people thought.
