1. The problem is to evaluate the expression $-1 + [-4]$. 2. The brackets around $-4$ indicate it is a single number, so the expression simplifies to $-1 + (-4)$. 3. Adding two negative numbers means moving further left on the number line. 4. Calculate $-1 + (-4) = -1 - 4 = -5$. 5. Therefore, the final answer is $-5$.