By what fractional part does four-fourths exceed three-fourths?

Four-fourths is represented as $\frac{4}{4}$ and three-fourths is represented as $\frac{3}{4}$.

To find the difference between four-fourths and three-fourths, we subtract the two fractions:

$$\frac{4}{4} - \frac{3}{4} = \frac{4-3}{4} = \frac{1}{4}$$

Thus, four-fourths exceeds three-fourths by $\frac{1}{4}$.

The fractional part by which four-fourths exceeds three-fourths is $\frac{1}{4}$.

Final Answer: The final answer is $\boxed{\frac{1}{4}}$