1. Explain the difference:

The definition of "namely" means that something or a situation is mentioned or quoted for reference or generalization.

The definition of "this is" refers to something or situation that is being mentioned or quoted at present.

Example:

I have two cars, which is my favorite one. I have two cars, which is my favorite. )

This is the book I have been looking for. )

2. Differences in usage:

-"That is" is often used to introduce, explain or quote something or situation mentioned earlier.

-"This is" is often used to introduce something or situation that is currently being discussed or mentioned.

Example:

I saw a beautiful sunset yesterday. This is something I will never forget. I saw a beautiful sunset yesterday. That's something I will never forget. )

-"This is an important meeting. Please pay attention. " This is an important meeting, please pay attention. )

3. Use environmental differences:

-"That is" is more commonly used in informal or oral contexts.

-"This is" is more commonly used in formal or written context.

Example:

-"He is a great musician. That's for sure! " He is a great musician. That's for sure! ) [Informal]

-"This is a major discovery and can contribute to scientific research." This is a great discovery and can contribute to scientific research. ) [formal]

4. Image difference:

"That is" usually causes a sense of distance, implying something or a situation far away from the speaker.

-"This is" usually has a sense of closeness, suggesting something or situation closer to the speaker.

Example:

-"Look at that beautiful sunset!" Look at that beautiful sunset! ) [Long-distance love]

-"This cake is delicious!" This cake tastes good! ) [closer]

5. Difference of influence scope:

-"That is" is more used to summarize or summarize general things, situations or concepts.

-"This is" is more used to emphasize the specific things or situations being mentioned at present.

Example:

-"Birds can fly, which is one of their unique characteristics." Birds can fly, which is their uniqueness. ) [general things]

-"This is the solution to the math problem." This is the answer to this math problem. )?