The function $f(x) = \ln(x)$ is defined only when the argument of the logarithm is positive, meaning $x > 0$. The logarithmic function cannot accept negative values or zero because the logarithm of a non-positive number is undefined in the real number system.

Thus, the correct domain of $f(x) = \ln(x)$ is $(0, \infty)$.

Therefore, the answer is (0, ∞).

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Would you like more details on logarithmic functions or have any other questions?

Here are five related questions for further exploration:

1. What is the range of $f(x) = \ln(x)$?
2. How would the domain change for $f(x) = \ln(x - 2)$?
3. What is the derivative of $f(x) = \ln(x)$?
4. How do you evaluate $\ln(1)$ and $\ln(e)$?
5. Can the logarithmic function $\ln(x)$ be extended to complex numbers?

Tip: The natural logarithm, $\ln(x)$, grows very slowly as $x$ increases.