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Grammarly checks faulty sentences for punctuation mistakes

We asked Grammarly to check some “faulty” sentences for punctuation mistakes, such as run-on or fused sentences (ROS), comma splice cases (CS), and sentence fragments (SF):

Grammarly performed well and managed to identify most cases of ROS, CS, and SF, as well as some other issues (e.g., a missing article and missing commas in the last example):


However the tool did miss a few errors:

the SF in the second sample (“Which is why…”)

the CS in the third sample (“…many reasons to work here, the weather is lovely…”)

the redundant preposition that starts the sixth sample, turning it into a sentence fragment (“By paying too much…”)


It also made a silly suggestion, in the last sample, to change the conjunction “and” to the indefinite article “an.”



Text used in the experiment: these sentences were devised by the convenor of an undergraduate writing course at Auckland University, to test student knowledge on common syntax and punctuation mistakes. To use these sentences for a classroom activity, visit Exercises. To download them as as a .docx file, click here.