Playfairciphers are block ciphers. The size of the block is m = 2. Two characters are encrypted together

From the definition of the block cipher, it is clear that every block cipher is a polyalphabetic cipher because each character in a ciphertextblock depends on all characters in the plaintext block.

 

in a palyfair encryption , because we are encrypting two by two letters together , so the ciphertext  only depends on one more letter in the plaintext , I do not understand why each character in cipher depends on all characters in plaintext