General antonyms:
* Listen
* Humble
* Quiet
* Hesitate
* Doubt
* Question
* Consider
Antonyms related to speaking:
* Converse
* Discuss
* Debate
* Engage
* Collaborate
Antonyms related to authority:
* Yield
* Submit
* Defer
* Respect
* Acknowledge
The best antonym will depend on the specific way "pontificate" is being used in the sentence.