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12 Types of Assumptions

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Assumptions are things that you hold to be true without proof that they are true. These are often required to get anything done in an environment of unknowns and uncertainties. The following are common types of assumptions.


Assumptions that are made automatically by an individual without realizing it. For example, assuming something about someone based on their appearance. This is a dangerous type of assumption because you are fully unaware that you are making things up.


Assumptions that go uncommunicated. For example, a sponsor of a product development effort who assumes the product packaging will be blue to reflect brand colors without ever stating this as a requirement or constraint. Unstated assumptions are a common reason for strategic, project and operational failures.


Assumptions that are pushed without any open conversation that allows them to be vetted. For example, an environment of groupthink whereby the assumptions of an ideology can't be questioned without severe social and/or economic penalties.


Assumptions based on lazy or unimaginative thinking. For example, a security organization that assumes the threats of the future will resemble recent threats.


Pragmatists are less concerned with whether something is actually true than with whether it is true for some practical purpose. Pragmatic assumptions are therefore designed to have some desirable outcome. For example, the assumption the customer is always right is not likely to be literally true but is useful to create a culture of respect for the customer by always taking the customer at their word.

Productive Assumptions

Productive assumptions are pragmatic assumptions that may be obviously untrue that are designed to motivate positive behavior. For example, assuming that your competitors and customers are extremely smart and innovative is a productive assumption that may drive you to constantly improve.

Unproductive Assumptions

Unproductive assumptions are any assumptions that decrease productivity, work quality, motivation or positive behaviors. For example, assuming that you are the most brilliant person in your field and that everyone else is dumb is an unproductive assumption as it is likely to cause you to underestimate your competition or just generally behave in an unlikable manner.

Likely Facts

By definition, an assumption is not a known truth. However, assumptions are often used to document things that are likely to be true based on evidence. For example, a construction project that assumes the project will not dig up any artifacts that trigger a legal requirement to preserve cultural heritage at a site. This can be based on evidence such as information about the known history of the site.


Assumptions can be predictions of the future such as probabilities or expert forecasts. For example, a ski hill that documents an assumption in a business plan that there will be at least 28 days of snow each season for the next 10 years based on climate predictions.


Assuming the worse possible outcomes. This is often done to argue against a strategy or policy. It is also commonly used to resist change in an attempt to preserve the status quo. For example, assuming that a project is doomed to fail such that it is a waste of time. Pessimistic assumptions can lead to negative behaviors such as defeatism. However, pessimistic assumptions can be useful in managing risks such as an aircraft designer who assumes that sensors will often fail such that the aircraft needs to remain fully safe when such failures occur.

Sour Grapes

Sour grapes is the pessimistic assumption that something that is difficult to get isn't worth having. This is an analogy from an old myth about a fox that sees grapes he can't reach so he assumes they must be sour.


Optimistic assumptions assume that things will be easy, low risk and fruitful. This tends to be dangerous as the real world is full of problems such that optimistic assumptions are usually wrong. However, in some cases optimistic assumptions can serve as productive assumptions. For example, optimistic assumptions encourage risk taking that may result in failures that build strengths and eventually result in great achievements.
Overview: Assumptions
Things that you hold to be true without proof that they are true.
Related Concepts


This is the complete list of articles we have written about assumptions.
Risk Taking
Sour Grapes
Status Quo
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