FEWER OR LESS?; DIFFERENCE OR DIFFERENTIATION?

The Encarta Dictionary Tools (Microsoft® Encarta® 2006. © 1993-2005 Microsoft Corporation) clarifies the correct distinctive usage for each term:

“fewer or less?

As a general rule, fewer is used with things you can count (fewer meetings, fewer people), whereas less is used with things you cannot count (less time, less money). The same difference applies to the use of fewer than and less than: fewer than twenty people, less than an hour. Designations of price, age, and measurement are normally regarded as singular, the idea being that, for example, “It cost less than ten dollars” has to do with an amount of money rather than a number of individual dollars. The use of less where the sense of countable number is strong (You may use the express lane if you have less than eight items) is relatively common, though many object to it.”

“difference or differentiation?

These two words do not share a single meaning, so careful writers avoid using them interchangeably. Difference denotes the quality of being different or an instance of this. Differentiation denotes becoming different in the course of development. My paper explores the difference [not differentiation] between the world of the adult and the world of the child. Conversely, do not use difference when differentiation is called for: studied the history of the differentiation [not difference] of Latin into vernaculars.”

Reference: Microsoft® Encarta® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.