【Artificial】 , 【Factitious】 , 【Synthetic】 and 【Ersatz】 all mean not brought into being by nature but by human art or effort or by some process of manufacture. They are not often interchangeable because of differences in some of their implications and in their range of application.

【Artificial】 is far more extensive in scope than the others. It may be applied to anything that is not produced by natural conditions but is in some sense a human creation.

• most of the inequalities in the existing world are 【artificial】
  —Russell
• the family is a natural society, the state is an 【artificial】 society

In law a corporation or an institution that may be the subject of rights or duties is called an 【artificial】 person in distinction from a human being, who is a natural person.

【Artificial】 is also applicable to something produced by human effort that has its counterpart in nature.

• Civilization may be said to have begun when the 【artificial】 heat and light of burning fuel were first used to supplement the natural heat and light of the sun.

【Artificial】 is applied also to things which imitate and sometimes serve the same purposes as something found in nature but which are of quite different origin and constitution and usually of inferior worth.

• 【artificial】 flowers of wax
• 【artificial】 jewels made from colored glass

【Artificial】 is also applicable to persons or to their acts, utterances, and behavior; it then implies lack of naturalness or spontaneity and often connotes affectation, conventionality, or formalism.

• set him to write poetry, he is limited, 【artificial】 , and impotent; set him to write prose, he is free, natural, and effective
  —Arnold
• the strained 【artificial】 romanticism of Kotzebue’s lugubrious dramas
  —Krutch

【Factitious】 is applied largely to such intangible things as emotions, states of mind, situations, relations, reasons, which are not naturally caused or are not the product of real circumstances but are invented or worked up for one’s own ends or purposes.

• create a 【factitious】 demand for shares of a stock
• the vogue was short-lived because 【factitious】
• his trick of doing nothing with an air, his salon manners and society smile, were but skin-deep, 【factitious】
  —Watson

they stood for Parliament and played the game of politics upon 【factitious】 issues
—H. G. Wells

【Synthetic】 is applicable to an end product so far removed from its ultimate natural source that it has become a wholly different thing.

• 【synthetic】 perfumes originally dug from the ground as coal

It is preferred to 【artificial】 when the noun modified denotes a class to which the thing in question actually belongs and it is free from the implication of inferiority that commonly clings to 【artificial】 ; thus, 【artificial】 silk is not silk since it is woven from 【synthetic】 fibers which are fibers man-made from substances that are not themselves fibrous.

To some degree differences in usage are purely idiomatic; thus, one ordinarily refers to 【synthetic】 rubber but 【artificial】 food coloring, 【synthetic】 fabrics but 【artificial】 flavoring.

【Ersatz】 is frequently used as a synonym of 【artificial】 or 【synthetic】 always, however, with the implication of use as a substitute; it is used chiefly with the name of a natural product.

• 【ersatz】 coffee
• 【ersatz】 butter
• 【ersatz】 wool

Thereby implying imitation and inferiority and, often, suggesting a cheap or disagreeable origin.

• the search for 【ersatz】   . . . materials was unceasing. Sugar from sawdust; flour from potato meal; gasoline from wood and coal
  —Gunther