Thinking is assumed to be abstract psychological processes that manipulate knowledge

Reasoning is the process of logical thinking. 

Reasoning research focuses on how a person either explicit or implicit premises. It is very important to understand the difference between the validity of a conclusion and its empirical truth because these distinctions have implications for the question of rationality. Validity refers only to whether a conclusion can be logically deduced from the premises. The validity of a conclusion is independent of whether that conclusion is true of the real word. For example, the following deductive argument is valid but not true: 

If the earth is flat you eventually would sale off the end.

The earth is flat.

Therefore, you would sale of the end if you travelled too far.

The conclusion is valid even though neither the premises nor the conclusion is true. Correctly judging the validity of logical arguments requires that the form of the arguments be separated from the content. The importance of this separation is that the abstract process of reasoning should be independent of the particular prior experiences that you have had with the content of the problems. That is, if people reason logically, they should have little difficulty separating validity from truth. Logic is the most extensively studied normative model of thinking. Logic is a formal system for deriving valid conclusions; that is, logic is the set of rules by which we can reach a valid conclusion about events or things. Formal logic specifies a prescription for correct reasoning. In that sense, formal logic is a normative model of thinking.  In our day-to-day affairs we usually considered the situation either by syllogistic reasoning or by conditional reasoning.

Syllogistic reasoning. In the case of syllogistic reasoning, consider the following argument to deny welfare assistance to homeless people:

All homeless people are poor.

Some poor people are lazy.

Therefore, some homeless people are lazy.

However, seductive this argument may be, it is invalid. The conclusion does not logically follow from the premises. The homeless people who are poor may not be the same for people who are lazy; thus the argument is not valid. 

Conditional reasoning. Conditional reasoning differs from the syllogistic reasoning in form. Conditional reasoning takes the form of if- then positions. For example, “If I win the next three cases for my law firm, I will receive a salary raise.” If fact, “I win the next three cases for my law firm,” then by the rules of the logic we can draw the conclusion: Therefore, “I will receive a salary raise.” We are familiar with conditional reasoning because we use it frequently in daily affairs.

Philip Johnson-Laird has offered a descriptive model of deductive reasoning that is called the mental model theory. Mental model theory assumes that reasoning begins with comprehension of the premises in syllogistic and conditional problems.

The decisions that we make in day-today life are rarely based on these reasoning. These reasoning are based on general premises, but our day to day decisions often are based on particular premises. From that particular thing we reach a conclusion, which is a decision about how to respond. For example I may notice that it is cloudy today and try to decide whether to take an umbrella when I leave. The particulate premise is “it is cloudy today” from which I moved to the secondary premise “some cloudy days in the past, it has rained.” Based on this premises, I conclude that “it may rain today” and decide to take my umbrella. This form of reasoning is known as inductive reasoning.

The conclusion to an inductive argument does not have the certainty or necessity of the deductive argument; consequently, inductive reasoning cannot be evaluated in terms of the logical validity of the conclusion. An induction is something that is likely to be true on the basis of past experience, but there is no guarantee that it will be absolutely true. Kahneman who pioneered research on decision making from inductive reasoning have suggested representativeness and availability wraths then probability in making decisions. 

The representative heuristic is a hypothetical process of making decisions based on the similarity of a current situation to past situations, and this similarity serves as the basis of judgements in lieu of consideration of such things as base-rates.

A slightly different heuristic strategy used in decision making is known as the availability heuristic. Where as representativeness is based on the similarity between events, a judgment based on availability is influenced by the ease with which something is brought to mind.

Our thinking is frequently influenced by availability rather than the more rational facts of probability. For many people, flying is very anxiety provoking, perhaps because stepping on an airplane brings to mind crashes. This is even more likely to happen following a major accident. You can see that availability is a powerful influence on our thinking, and you can imagine that it could enter into crucial decision processes in a negative way. Suppose a bad stomach virus is going around and you acquire what appear to be the appropriate symptoms. Nonetheless, you visit a physician she has seen hundreds of cases of stomach virus in the last week and decided that is your problem without further examination. Unfortunately, Pneumonia sometimes produces similar symptoms fever, aches, and nausea. Diagnosis of stomach virus based on availability could have disastrous consequences if the pneumonia is left untreated.

This final example illustrate the potential importance of using a rule based process in our thinking, but the psychology of reasoning once again demonstrates that such is not always the case.