In the given recursively defined arithmetic sequence, we have:
- \( a_1 = 4 \)
- \( a_n = a_{n-1} - 5 \)
The common difference \( d \) can be identified from the recursive formula. Since each term is obtained by subtracting 5 from the previous term, we can say that the common difference is:
\[ d = -5 \]
So, the common difference in this arithmetic sequence is \( -5 \).