When writing formal pieces, some pitfalls in the punctuation are easy to avoid once you know them. Punctuation marks such as the comma, the semi-colon, the colon and the period are useful for organising phrases and clauses, facilitating the reading, and disambiguating. However, these marks are also liable to underuse, as in the case of run-on sentences; misuse, as in the comma splice; and overuse, as it often happens with the Oxford comma.