When one argues deductively, one asserts (among other things) that the set consisting of the premises and the denial of the conclusion is inconsistent. In other words, one asserts that it’s necessary that at least one member of the set be false. “What else does one assert when arguing deductively?” you ask. One asserts the premises. Suppose I argue as follows:

1. All dogs are mammals.
2. All mammals are animals.
Therefore,
3. All dogs are animals.

I’m making four assertions. First, I’m asserting that all dogs are mammals. Second, I’m asserting that all mammals are animals. Third, I’m asserting that it’s impossible for 1 and 2 to be true while 3 is false. Fourth, I’m asserting that all dogs are animals. The fourth assertion is based on the other three.

When one argues inductively, one concedes that the set consisting of the premises and the denial of the conclusion is consistent, but insists that it’s unlikely that all of its members are true. In other words, one asserts that it’s probable that at least one member of the set is false. “What else does one assert when arguing inductively?” you ask. The same as before: One asserts the premises. Suppose I argue as follows:

1. Most college professors are progressives.
2. Leslie is a college professor.
Therefore,
3. Leslie is a progressive.

I’m making four assertions. First, I’m asserting that most college professors are progressives. Second, I’m asserting that Leslie is a college professor. Third, I’m asserting that it’s improbable (i.e., unlikely) that 1 and 2 are true while 3 is false. Fourth, I’m asserting that Leslie is a progressive. As before, the fourth assertion is based on the other three.

How does one criticize an argument? In general, one criticizes an argument by denying at least one of the arguer’s assertions. In the case of the second argument, I may deny either that most college professors are progressives or that Leslie is a college professor. (The arguer may be mistaken about Leslie’s occupation.) I may also deny the assertion that it’s unlikely that all the members of the set consisting of the premises and the denial of the conclusion are true. In other words, I may deny that the truth of the premises makes the truth of the conclusion probable. Probability, unlike necessity, is a matter of degree, so the most that can be said about any inductive argument is that it’s strong. Here is a (comparatively) strong inductive argument:

1. 99.9% of college professors are progressives.
2. Leslie is a college professor.
Therefore,
3. Leslie is a progressive.

Note that it’s possible for 1 and 2 to be true while 3 is false. Here is a weaker inductive argument:

1. 75% of college professors are progressives.
2. Leslie is a college professor.
Therefore,
3. Leslie is a progressive.

Note the tradeoff. One strengthens the argument by increasing the percentage of college professors who are progressives, but at the cost of making the premise false. In general, one should say as much as one truthfully can.