In many occasions the words type and class can be used interchangeably.
Type and class are words used in categorizing, grouping or clustering items of similar trait(s).
There are four possible combinations in categorizing an item
- (1:1) One class which has only one item.
- (1:many) One class which has many items.
- (Many:1) Many classes, each having only one item.
- (Many:[1 or Many]) Many classes, each having one or more items.
Therefore, these are the possible ways to use the words class, type or category:
- This category of a person. (1:1)
- This type of a person (1:1)
- This type of persons (1:many)
- This types of a person (Many:1)
- These types of persons (Many:[1 or Many])
Orthogonally, the case of [many:1] should be ignored, and should be rolled into [Many:[1 or Many]].
Frequently, we deliberately wish to be agnostic to the number of items in a class/type. The reason being, when we wish to develop statistical perspectives that are not biased by our foreknowledge of its number of items - even when we think we know there is highly probable only one item in a particular type, we presume the possibility of the type having many items. In such a situation, we would have to say "this type of items".
Similar forgiveness that we deserve from the situation that while we say, "there is one car on the road", we would say "there are no cars on the road".
- This type of a selfish person should never exist on this planet.
- The type of houses in the Midwest are often boring and unimaginative, compared to the diverse types of houses in the Northeast.
The one important rule of typing or categorization is defining the trait(s) of similarity (often called characteristics of a class).
The act of boiling up or percolating the characteristic traits out of an item is often called characterization. For example, your IC designer would ask you, "Have you characterized the process yet?".
Or your process planner might ask you, "Have you characterized the performance of the WIP products yet, so that we could price them into our marketing categories?"
Therefore, anyone who says that the word type is redundant has not have sufficient exposure to industrial and taxonomic importance of the word.
Is it the column, the row, the valency, the number of stable valencies, similar ambiguities, the number of isotopes, the number of neutrons, the difference between the number of neutrons and protons, the absence of neutrons, something within their quantum behaviour, or chemical behaviour, etc ?