Hi Yusuke, They have different connotations. Tongue-tied means being unable to speak due to shyness or embarrassment whereas speechless means being unable to speak due shock, surprise, amazement or even annoyance, depending on the context. Hope that helps!

There is a difference. "Tongue-tied" can be caused by nervousness or worry or confusion. "Speechless" usually is caused by shock or surprise, or from being extremely offended.

Imagine if your tongue was actually tied. You can't really talk, but you can still make sounds. This can be compared to a guy stuttering because he saw a pretty girl. It's because he's either shy or embarrassed. However, if you're speechless, then no sounds can come out. A person can become speechless when they are in shock. Their throat closes up, and no sound can come out. It can be because of anger, fear, jealousy, etc. I hope that clarifies it a little more.

Yes, they are the same.

I would say it depends on the situation and on how you'll be using it in a sentence😊