Here's why:
* Syllable count: Tankas are known for their specific syllable structure: 5-7-5-7-7.
* Quatrains: While a tanka has five lines, the first three lines often form a quatrain that sets the scene or introduces the subject matter.
* Popularity: Tankas are a popular form of Japanese poetry that have gained international recognition.
However, it's important to note that other poetic forms also utilize quatrains and have syllable counts. Some examples include:
* Haiku: A three-line poem with a 5-7-5 syllable structure.
* Limerick: A five-line poem with an AABBA rhyme scheme and a specific syllable count (8-8-5-5-8).
Therefore, without more context about the specific poem or the syllable count, it's hard to definitively say which poetic form it is. However, based on your description, a tanka is the most likely candidate.