How It Differs

I'm sure you can see now how very different deduction and induction are, and how easily you can tell the difference. Remember, if you are thinking deductively; your second point will always comment on the subject or predicate of the first. If it does not so comment, you should be able to classify it by the same plural noun as the first, to test that you have a proper inductive grouping.

To demonstrate, I recently ran across two so-called deductive fallacies in a logic book, which went as follows:

All Communists (Ire proponents of socialized medicine

Some members of the administration ore proponents of socialized medicine

Therefore, some members of the administration are Communists.

All rabbits are very fast runners

Some horses are very fast runners

Therefore, some horses rabbits.

In both cases, I'm sure you will instantly be able to see that the second point does not make a comment on the first point, so these ideas cannot be deductively related. What the second point does do in each case is to add another member to the classification (plural noun) established in the first point. Placing ideas in classes is defining them by a plural noun, and you know that that is induction.

To test yourself, suppose I say to you:

Japanese businessmen are escalating their drive for the Chinese market.

Can you pick which of the next two points relates inductively to this, and which one deductively?

The fact that American businessmen will soon be entering the market is sure to stimulate them further.

American businessmen are escalating their drive for the Chinese market.

Clearly the first is deductive and the second inductive.

Note that with inductive ideas you generally either hold the subject constant and vary the predicate, or hold the predicate constant and vary the subject. For example, you could say:

Japanese businessmen are escalating their drive for the Chinese market.

American businessmen are escalating their drive for the Chinese market.

German businessmen are escalating their drive for the Chinese market.

The smart money is moving into China.

or you could say:

 Japanese businessmen escalating their drive for the Chinese market.

Japanese businessmen are escalating their drive for the Indonesian market.

Japanese businessmen are escalating their drive for the Australian market.

Japanese businessmen are moving aggressively into Southeast Asia.

Look at yet a third example:

Japanese businessmen arc escalating their drive for the Chinese market.

Japanese businessmen are escalating their drive for the Icelandic market.

Japanese businessmen are escalating their drive for the Peruvian market.

What is the same about China, Iceland, and Peru-other than the fact that Japanese businessmen are entering their markets? Nothing. These facts are not related, and thus cannot inspire you to draw a more general insight. In stating them you are simply passing along news, and there is no place for news in a document whose purpose is to communicate your thinking.

This distinction between news and thinking is an important one to bear in mind, since the fact that the "news" is true tends to lead some writers to believe that such points can be legitimately included in a document. Remember back: the only justification for including a point in a document is that, together with others, it helps to explain or defend a higher point. This higher point can legitimately be derived front a grouping of ideas only if the ideas in the grouping are properly related, either inductively (similar subjects or predicates) or deductively (the second point comments on the first).

To summarize, a deductive relationship is established if the second point comments on the first, leading to a "therefore" conclusion. Inductive relationship resides in the structure of the sentence. Look for similarity in either the subjects or the predicates, and draw your inference based on that similarity. If there is no similarity, you can draw no inference, and the points do not belong in the document.

It is interesting to note that whether you couple the ideas to form an inductive grouping or the beginning of a deductive line of reasoning, your mind automatically expects either a summarizing statement or a "therefore" point. This expectation of the mind for deductive and inductive arguments to be completed often leads the reader to project his thinking ahead, to formulate what he thinks your next point will be. If his projected point is different from your actual point, he can become both confused and annoyed. Consequently, you want to make sure that he will easily recognize the direction in which your thinking is tending by giving him the top point before you state the ideas.