Arigato vs. Arigatai: Meaning & Usage

Arigatou (ありがとう/有難う), also spelled as Arigato, is a Japanese word that many overseas people know, meaning Thank you.

Meanwhile, Arigatai (ありがたい/有難い) is a similar word to it equivalent to grateful/thankful in English, which I think may confuse Japanese learners.

Arigato (ありがとう) vs. Arigatai (ありがたい)

According to Goo’s Japanese dictionary, while Arigato derives from Arigatai,

the original form of Arigatai is the old word Arigatashi (有難し), which reads as difficult to exist or rare.

Usage

As with Thank you, we usually say Arigato when we want to express gratitude.

In contrast, as Arigatashi reads, we use Arigatai when we appreciate what rarely happens or when something conveniently happens, like these.

• 有難い助言、本当にありがとうございます can translate into English as Thank you very much for your precious advice.
• 雨が止んで有難い → Thankfully, it’s stopped raining.

In the above cases, you can’t use Arigato in place of Arigatai. The phrase 有難う助言 and the sentence 雨が止んで有難う are unnatural. 

But as the origin of Arigatai and Arigato is the same, they can sometimes be replaced, like below.

• 手伝ってくれて有難い, meaning I am grateful for your help → 手伝ってくれて有難う is natural and reads as Thank you for your help.

However, compared to the latter, the former sentence 手伝ってくれて有難い implies that the speaker didn’t expect help.