1. **Stating the problem:** A couple has five sons, and we want to find the probability that their next baby will be a daughter. 2. **Understanding the problem:** The gender of each child is generally considered an independent event with two equally likely outcomes: son or daughter. 3. **Formula used:** The probability of having a daughter in any single birth is $$P(\text{daughter}) = \frac{1}{2}$$ 4. **Important rule:** The gender of previous children does not affect the probability of the next child’s gender because each birth is independent. 5. **Applying the rule:** Regardless of having five sons already, the probability that the next baby is a daughter remains $$\boxed{\frac{1}{2}}$$ 6. **Answer:** The correct choice is option 4, $\frac{1}{2}$.