Amplification & Depreciation
a general name for anything that expands or reduces effect: figures of speech, vocabulary, topics, arrangement of arguments, etc.
Aristotle
[Amplification] is to increase the rhetorical effect and importance of a statement by intensifying the circumstances of an object or action.

Examples

 Leonardo di Caprio urges action on global warming at the United Nations Climate Summit, 2014
Di Caprio amplifies with accumulatio, anaphora, hyperbole, movere, repetition.
Barack Obama urges reform of gun laws at the White House, October, 2015
Obama amplifies with anaphora, enargia, epistrophe, metaphor, metonymy, polysyndeton, repetition, tricolon.
 Stephen Fry condemns the Roman Catholic Church at the Intelligence Squared Debate, October, 2009
Fry amplifies with accumulatio, alliteration, analogy, anaphora, anecdote, climax, dialogismus, dysphemism, enargia, hyperbole, movere, metaphor, paradox, parody, personification, polysyndeton, repetition, ridicule, tricolon.

Purpose

Aristotle
All men employ extenuation or amplification whether deliberating, praising or blaming, accusing or defending.
Amplification and depreciation are discursive strategies that seek to move audiences to extremes: to urgency of action, adulation or contempt for a situation or subject, etc. They often feature in deliberative and epideictic oratory:

  • Di Caprio wants us to fear global warming enough that we act (deliberative oratory).
  • Obama wants us to stop accepting gun deaths as routine and act to prevent them (deliberative oratory).
  • Fry wants us to hate the senior clergy and practices of the Roman Catholic Church (epideictic oratory).

Usage

Blaise Pascal
The heart has its reasons which reason knows nothing of.
Amplification and depreciation are discursive macro-strategies: They depend on skilfully using and combining appropriate figures of speech,  like the speakers above do.

Decide first on your message. You may want your audience to admire, love, fear, hate something; to take action, to think or believe something; to grasp the size, intensity, similarity, utility, importance, urgency, value, goodness, badness of something. The strategies and figures described here and on other pages can help.
Aristotle's Advice on Amplifying Praise
  • Show someone to be the first or only person to have achieved something.
  • Show someone or their contributions to be superior to others.
  • Show someone to be repeatedly superior.
  • Show someone's contributions to be deserved: through effort, against adversity, without advantage, etc.
  • Show someone or their contributions to be comparable to or better than other 'greats.'
Depreciation uses similar strategies or inverts them. For example, we can show someone to have usually failed or rarely excelled, or to have excelled through unfair advantage.
Amplifying with Climax
To amplify with climax, arrange words, clauses or sentences in increasing importance or force. Climax may combine with asyndeton, polysyndeton, parallelism, tricolon or dysphemism.
Cicero
It is a crime to put a Roman citizen in bonds; it is the height of guilt to scourge him; little less than parricide to put him to death: what name, then, shall I give to the act of crucifying him?
Barack Obama
When we send our young men and women into harm's way, we have a solemn obligation not to fudge the numbers or shade the truth about why they're going, to care for their families while they're gone, to tend to the soldiers upon their return, and to never ever go to war without enough troops to win the war, secure the peace, and earn the respect of the world.
The above examples summit mount climax by planting the flag of triumph at the peak. Put the most emphatic elements in final position. Notice these include preposition phrases (of + emphatic word). These are common in emphatic endings.
M.L. King
George Wald
This note was a promise that all men, yes, black men as well as white men, would be guaranteed the unalienable rights of life, liberty and the pursuit of happiness.
I think we've reached a point of great decision, not just for our nation, not only for all humanity, but for life upon the earth.
Amplifying with Conclusions
We can amplify by adding conclusions after our main ideas or arguments. Brief conclusions summarize, amplify and repeat what we have said. The technical name is epitasis. Single-word conclusions do this even more emphatically. 
A parent scolds her children
Gollum protests his innocence
The Lord of the Rings: The Return of the King, New Line Cinema, 2003
Look at the state of this kitchen! Everything is a mess. The worktop is filthy. The floor is sticky. I want it cleaned. Everything!
Amplifying with Heapings-Up
'Heapings-up' is not a Classical term but accommodates many Classical figures of amplification that combine with others. We can use these to achieve pathos effects by repeating pleas and piling them up like a rolling snowball to maximize impact. Stephen Fry does this in the video above. Other ways we can heap-up:
  • Lay out your arguments and descriptions with accumulating force - climax & accumulatio
  • Use language to repeatedly move the emotions - movere 
  • Exaggerate for effect - hyperbole
  • Repeat words or phrases with similar meanings - conduplicatio
  • Repeat words with different meanings but similar effects - congeries
  • Repeat words or phrases superfluously for effect - pleonasm
  • Ask repeated rhetorical questions - erotema & epiplexis
Christopher Hitchens
The truth never lies but when it does lie it lies somewhere inbetween.
(congeries)
Depreciating vs. Negating
We can depreciate things by making them seem less important, worrisome, relevant, interesting, etc. Depreciation is theoretically a middle-ground between assertion and negation. Compare:
Assertion
Saddam Hussein's Iraq has weapons of mass destruction.
Depreciation
Saddam Hussein has only a handful of weapons of mass destruction which are anyway obsolete.
Negation
Saddam Hussein's Iraq does not have weapons of mass destruction.
Depreciating with Understatement
We can depreciate by understating things. The figures of euphemism, litotes and irony may be used for this.
Depreciating with Tapinosis
We can depreciate more stridently with dysphemism or tapinosis - using names to diminish importance.
Christopher Hitchens describes Prince Charles:
Charles Windsor, Prince of Piffle

Slang for Professions
beak/wig - judge
hack - journalist
shrink - psychiatrist
sawbones/quack - doctor
bean-counter - accountant
ambulance chaser - personal injury lawyer
Monty Python describes 'flesh wounds'
Monty Python and the Holy Grail, EMI Films, 1975