In rhetoric, parallelism involves the juxtaposition of two or more identical or equivalent syntactic constructions, especially those expressing the same sentiment with slight modifications, introduced for rhetorical effect.

Bust of Gaius Julius Caesar in the National Ar...

Bust of Gaius Julius Caesar

In short, parallelism means giving two or more parts of the sentences a similar form so as to give the whole a definite pattern.

Parallelisms of various sorts are the chief rhetorical device of Biblical poetry in Hebrew. In fact, Robert Lowth coined the term parallelismus membrorum (parallelism of members, i.e. poetic lines) in his 1788 book, Lectures on the Sacred Poetry of the Hebrew Nation.

In addition, Chinese poetry uses parallelism in its first form. In a parallel couplet not only must the content, the parts of speech, the mythological and historical and geographical allusions, be all separately matched and balanced, but most of the tones must also be paired reciprocally. Even tones are conjoined with inflected ones, and vice versa.

Examples of parallelism include:

“Veni, vidi, vici.” (I came, I saw, I conquered)
– Julius Caesar

“The inherent vice of capitalism is the unequal sharing of blessing; the inherent virtue of socialism is the equal sharing of miseries.”
– Churchill

“But let judgment run down as waters, and righteousness as a mighty stream.”
– Amos

“We charge him with having broken his coronation-oath – and we are told that he kept his marriage-vow! We accuse him of having given up his people to the merciless inflictions of the most hard-hearted of prelates – and the defence is that he took his little son on his knee and kissed him. We censure him for having violated the Petition of Right – and we are informed that he was accustomed to hear prayers at six o’clock in the morning.”
– Macaulay