The theory of planned behavior (TPB) and the theory of reasoned action (TRA) both explain how beliefs shape intentions and how intentions relate to behavior. The key difference is that TPB adds perceived behavioral control as a factor influencing intention and, in some circumstances, behavior; TRA focuses on attitudes, perceived social expectations, intentions, and actions when the person has sufficient control over acting.
Background: how the theories are related
TRA came first as a framework for explaining deliberate behavior. It was developed by Martin Fishbein and Icek Ajzen, whose work connected a person’s intention to act with two main influences: their evaluation of the behavior and their perception of what important people expect. The framework is especially suited to actions that a person can choose to perform or avoid.
TPB is an extension of TRA, developed by Ajzen to address a limitation: many actions are not entirely under a person’s control. Someone may intend to take an action but lack time, access, ability, money, or another necessary resource. TPB therefore includes perceived behavioral control, or a person’s judgment about how easy or difficult performing the behavior is likely to be.
The theories are closely related, not competing explanations with wholly different foundations. TPB retains TRA’s attitude, subjective norm, and intention components, while adding a construct intended to account for constraints on action. Researchers and students may encounter both in social psychology, communication, health research, marketing, and other fields that study decisions and behavior.
What the theory of reasoned action means
In TRA, a person’s intention to perform a specific behavior is predicted by two broad factors:
- Attitude toward the behavior: whether the person evaluates performing that action favorably or unfavorably.
- Subjective norm: the person’s perception of whether relevant people approve, expect, or support the action.
Intention is the person’s readiness or plan to carry out the behavior. TRA treats intention as the most immediate predictor of action, assuming the behavior is sufficiently voluntary. The theory does not say that people always act on their intentions. Instead, it gives a model for understanding why intention may form and when it is likely to relate to behavior.
Attitudes and subjective norms are grounded in beliefs. A person may believe an action will produce a useful outcome and value that outcome, leading to a more favorable attitude. They may also believe that people whose opinions matter approve of the action. These are distinct routes: a student might personally see a study group as helpful while also believing their classmates expect them to attend.
What the theory of planned behavior means
TPB includes the TRA components—attitude, subjective norm, and intention—and adds perceived behavioral control. This refers to a person’s perception of their ability to perform the behavior, including how much it seems to depend on their own capacity and on factors outside their control.
Perceived control can influence intention: a person may be more willing to act if the action seems manageable. It can also help predict behavior directly when the perception reflects actual control reasonably well. For example, someone who believes they can get to a meeting and actually has reliable transport may be more likely to attend. If their perception is inaccurate, perceived control may be a weaker guide to what happens.
Perceived behavioral control is not simply another name for intention, and it is not the same as objective control. It is a judgment about control. Researchers may separately consider actual constraints, such as whether a required resource is available, because confidence alone cannot remove a real barrier.
Side-by-side comparison
| Feature | Theory of reasoned action | Theory of planned behavior |
|---|---|---|
| Core purpose | Explain intention and voluntary behavior | Explain intention and behavior when control may be limited |
| Attitude | Included | Included |
| Subjective norm | Included | Included |
| Perceived behavioral control | Not a separate component | Included |
| Role of intention | Central link to action | Central link to action, alongside perceived control in relevant cases |
| Best fit | A behavior largely under the person’s choice | A behavior that may be affected by capability or constraints |
This is a conceptual comparison, not a claim that one theory always predicts better. How useful either model is depends on the behavior, how its components are measured, and whether the study captures important influences accurately.
How the models work: a student example
Consider a student deciding whether to attend a voluntary study group. Under TRA, the student’s attitude might depend on whether they expect the group to clarify difficult material and whether they value that benefit. Their subjective norm might reflect whether friends, classmates, or an instructor seem to support attendance. Together, those considerations help shape the student’s intention to go.
TPB considers the same factors, then asks whether the student believes attendance is within reach. A conflicting class, a long commute, limited transport, or uncertainty about where the group meets could reduce perceived control. The student may therefore intend to attend less strongly, even while viewing the group positively and believing others approve. If the obstacle is real, it may also prevent attendance after an intention has formed.
The example illustrates why it matters to define the behavior precisely. “Study more” is broad; “attend the scheduled study group this week” is more specific. A clear behavior, context, and time frame make it easier to connect beliefs, intentions, and observed actions in a coherent analysis.
When to use each theory in a course assignment
Choose TRA when the behavior is substantially voluntary and the question centers on how personal evaluation and perceived social expectations relate to intention. It can be a suitable starting framework for a decision that the person can generally make without major practical barriers.
Choose TPB when a person’s perceived ability, access, or constraints are likely to matter. It is often the more natural framework for studying actions that require resources, skills, opportunities, or coordination. The added component is useful only if it is relevant to the research question; adding a construct without a reason can make a model less clear rather than more informative.
For a paper or research proposal, ask:
- Is the behavior clearly defined and reasonably specific?
- Can people freely perform it, or do resources and circumstances limit them?
- Does the question concern personal evaluation, social pressure, perceived ability, or a combination?
- Can the proposed measures distinguish intention from actual behavior and perceived control from real constraints?
Common mistakes and limitations
A common mistake is to describe TPB as a replacement that discards TRA. It is better understood as an extension: TPB keeps the earlier model’s main elements and adds perceived behavioral control. Another mistake is to treat subjective norm as objective social pressure. It is the individual’s perception of expectations, which may differ from what other people actually think.
Students also sometimes assume intention guarantees behavior. Both frameworks allow for a gap between planning and action. Circumstances can change, barriers can intervene, and a person may not follow through. In TPB, perceived control helps account for some of this, but it cannot capture every obstacle or guarantee accurate prediction.
Neither framework automatically includes every influence on behavior. Habit, emotion, identity, organizational conditions, and broader social or material factors may matter in a particular case. That does not make the theories useless; it means researchers should explain why a model fits their question and consider whether important influences fall outside its scope.
How to remember the difference
Use the phrase “planned adds control” as a quick memory aid. Both theories include attitudes, perceived social expectations, and intentions; the planned-behavior model adds perceived behavioral control. If the action is largely a matter of choosing, TRA may be enough. If the ability or opportunity to act is central, consider TPB.
In an exam answer, state the relationship before listing components: TPB extends TRA to address behavior that is not fully under voluntary control. Then name the shared factors and identify perceived behavioral control as the addition. This structure answers the comparison directly and avoids implying that the models are unrelated.
Frequently Asked Questions
Is the theory of planned behavior an extension of the theory of reasoned action?
Yes. TPB retains TRA’s attitude, subjective norm, and intention components, and adds perceived behavioral control to address constraints on action.
What is the main difference between TRA and TPB?
The main difference is perceived behavioral control. It is a distinct component in TPB, but not in TRA.
Does the theory of reasoned action include perceived control?
Not as a separate component in its standard formulation. Its central predictors of intention are attitude toward the behavior and subjective norm.
Does perceived behavioral control mean actual control?
No. It means a person’s perception of how much control they have. Researchers may also need to examine actual resources and barriers.
Which theory should I use for a college assignment?
Use the model that fits the behavior and research question. TRA may fit a largely voluntary choice; TPB is often more suitable when perceived ability or practical constraints are important. Define the behavior and explain your choice.
Do either of these theories say that intentions always become actions?
No. Intention is an important predictor, not a guarantee. Circumstances, opportunity, and other influences can prevent someone from acting as intended.