1. The problem is to calculate $2 - 4$. 2. We use the basic arithmetic subtraction rule: subtract the second number from the first. 3. Calculate $2 - 4$. 4. Since $4$ is greater than $2$, subtracting $4$ from $2$ results in a negative number. 5. The calculation is $2 - 4 = -2$. 6. Therefore, the final answer is $-2$.