Logical strength is the degree of support that the premises confer on a conclusion—the degree to which the premises, if true, make it likely that the conclusion is true as well. The stronger an argument is, the tighter the relationship between its premises and conclusion; the weaker it is, the looser the relationship.
The application of inductive logic to a set of premises to develop one or more hypotheses is at the heart of the intelligence analysis process. The hypothesis is a tentative explanation, subject to further testing, of a situation, process, threat, or activity of interest. Developing useful hypotheses requires skill in applying logical reasoning to a set of premises that have been developed from data organized and integrated for this purpose.
The critical aspect of this skill is that of organizing a set of premises into an argument that leads to an explanation that is based on the facts summarized in the premises, but that projects the explanation beyond these facts alone. That is, the analyst develops a hypothesis that fills in missing gaps to provide a more complete and more useful explanation. The set of hypotheses thus developed serves as the basis for guiding the collection of additional information to fill in the gaps with facts rather than conjecture. The establishment of logical relationships enables the intelligence analyst to link information to premises, premises to hypotheses, and hypotheses to inferences that can be acted on with confidence. The logical relationships are necessarily inductive in nature— going from the specifics to the general, permitting discovery of what was previously unknown. It is the tightness of this logic that provides the necessary discipline for the ultimate development of useful, valid inferences.
Think of logical strength in a more layman way like this. Its a measure of the likelihood that the conclusion of an argument is true given that its premises are all true. The easiest way to determine the logical strength of an argument is to ask what the likelihood is of the conclusion’s being false assuming that the premises are all true.
For example, the argument,
All men are mortal.
Socrates is a man.
Therefore, Socrates is mortal
has a very high degree of logical strength because the likelihood that the conclusion is false given that the premises are all true is nil. By comparison, the argument,
Hardly any men are honest.
Socrates is a man.
Therefore, Socrates is honest.
This has a low degree of logical strength because the likelihood that the conclusion is false given that the premises are all true is high.