Perpendiculum rectum pendet, sed canalis declivis est.

The plumb line hangs straight, but the conduit slopes downward.

Breakdown of Perpendiculum rectum pendet, sed canalis declivis est.

• esse: to be
• sed: but
• rectus: straight
• pendere: to hang

Questions & Answers about Perpendiculum rectum pendet, sed canalis declivis est.

Why is rectum used, not rectus?

Because perpendiculum is a neuter singular noun, and the adjective has to agree with it.

• perpendiculum = neuter singular
• rectum = neuter singular form of rectus, recta, rectum

So rectum matches perpendiculum in gender, number, and case.

If the noun were masculine, you would expect rectus; if feminine, recta.

What case is perpendiculum?

Here perpendiculum is nominative singular, because it is the subject of pendet.

The basic structure is:

• perpendiculum = the subject
• pendet = hangs
• rectum = describes the subject

So the first clause means something like the plumb line hangs straight/upright.

Is rectum an adjective or an adverb here?

It is best understood as an adjective, not an adverb.

It agrees with perpendiculum, so it is describing the subject: the plumb line is straight/upright while hanging.

A native English speaker may expect an adverb because English often says things like hangs straight, where can feel adverb-like. But in Latin, is still an adjective agreeing with the noun.