Rhetorical Functions in Academic Speaking: Classifying / categorising

When we classify, we arrange members of a group. For example, if we take the following list:

Physics, Chemistry, Biology, French, German, Spanish.

It is quite clear that we have two different types of word. We have science subjects and languages. So it is simple to divide the list into two:

Physics, Chemistry, Biology,

AND

French, German, Spanish

When we are classifying, we often need to say what our classification is and how we are making it.

Examples

Read the following text.

We can divide lavas into two contrasting types, acid and basic. Acid or siliceous lavas have a high silica content, about 70 to 75 per cent, and are stiff or viscous. They move slowly over the surface and solidify close to the vent. Basic lavas have a silica content of about 50 per cent. They are dark colored and fluid, and they flow more easily at lower temperatures and reach a greater distance from the crater than do acid lavas.

Adapted from This earth of ours, p3.

What is the text classifying? Lavas.
How many types are there? 2
What are the two types? Acid and basic.
How do we make the distinction? The amount of silica present.

Language

The tables below show some of the most common language used in sentences which have classification as their purpose.

There are	two	types kinds classes categories sorts varieties	of lava	: acidic and basic. . These are acidic and basic.
The				are acidic and basic.

Lava

consists of
comprises
can be divided into

two

categories
classes
kinds
types
varieties

. These are acidic and basic.
: acidic and basic.

Acidic and basic are

classes
kinds
types
categories
varieties

of lava.

We can classify lava

according to
on the basis of
depending on

amount of silica present.

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