What is a monster? A being whose survival is incompatible with the existing order.
Interpretation
A monster is defined as something that cannot coexist within the current societal structures.
Denis Diderot's quote reflects on the nature of monsters as beings that challenge or disrupt the established norms and order of society. This could apply to individuals or ideas that are seen as threats because they do not conform to the accepted ways of living or believing, ultimately leading to conflict between the entity and its environment.
In practice
In a debate about societal norms, one might reference this quote to illustrate how individuals or ideas that challenge the status quo are often labeled as 'monsters'.
The arbitrary rule of a just and enlightened prince is always bad. His virtues are the most dangerous and the surest form of seduction: they lull a people imperceptibly into the habit of loving, respecting, and serving his successor, whoever that successor may be, no matter how wicked or stupid.
This root [the potato], no matter how much you prepare it, is tasteless and floury. It cannot pass for an agreeable food, but it supplies a food sufficiently abundant and sufficiently healthy for men who ask only to sustain themselves. The potato is criticized with reason for being windy, but what matters windiness for the vigorous organisms of peasants and laborers?
Do you see this egg? With this you can topple every theological theory, every church or temple in the world.
There are three principal means of acquiring knowledge... observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination.
In order to get as much fame as one's father one has to much more able than he.
All abstract sciences are nothing but the study of relations between signs.
So much universe, and so little time.
Over and over again, stories in women's magazines insist that women can know fulfillment only at the moment of giving birth to a child. They deny the years when she can no longer look forward to giving birth, even if she repeats the act over and over again. In the feminine mystique, there is no other way for a woman to dream of creation or of the future. There is no other way she can even dream about herself, except as her children's mother, her husband's wife.
Before me things created were none, save things Eternal, and eternal I endure. All hope abandon, ye who enter here.
My father was a man of principle who found his principles confirmed in the unremitting failure which they brought on him.
This generation of Americans has a rendezvous with destiny.
Big Brother in the form of an increasingly powerful government and in an increasingly powerful private sector will pile the records high with reasons why privacy should give way to national security, to law and order, to efficiency of operation, to scientific advancement and the like.
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