I'm studying(and clearing my head) about block cipher. I started from Caesar Cipher which can be considered as a kind of substitution cipher (if my understanding is right).
And an ideal substitution cipher (in 26 alphabets) is the two functions $E(x,k)$ and $D(x,k)$ where $0 \leq k < 26!$. And given $k$, one of the bijection(substitution) functions is (uniformly)selected and used to substitute a letter.
What I thought here is that this is also a block cipher. (1 letter is 1 block) I read https://en.wikipedia.org/wiki/Substitution_cipher and it says
Although the number of possible keys is very large ($26! \approx 2^{88.4}$, or about 88 bits), this cipher is not very strong, and is easily broken. Provided the message is of reasonable length (see below), the cryptanalyst can deduce the probable meaning of the most common symbols by analyzing the frequency distribution of the ciphertext—frequency analysis.
I feel this description is talking about the problem of ECB mode in block cipher.
So my understanding so far is that substitution cipher can be considered as a block cipher. But I'm wondering if a block cipher is always substitution cipher.
What is the difference between them in general.