Critical Thinking

Assumptions are another type of claim which you will find in some arguments, and they come in two forms: explicit and implicit.

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Explicit Assumptions

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An explicit assumption is a claim put forward which lacks supportive evidence. These claims often function as essential premises in an argument:  

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[P1] Most people in England believe in God.

[C] Therefore we ought to promote the teaching of religion in English schools.

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The ‘reasonable’ assumption here - ‘most people believe in God’ - is explicit and is used to support the conclusion that religion should be taught in schools. But the initial claim is only stated; no evidence or reasons are provided to support it.

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Implicit Assumptions

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The previous conclusion: ‘therefore we ought to promote the teaching of religion in schools’ doesn’t really follow from the initial premise.

The ‘implicit’ (i.e. unstated) assumption that it does follow is even less convincing than the previous explicit one, for this argument would only be valid if we accept the implicit premise that:

[P2] ‘the majority of people believing in something is evidence enough for the promotion of that thing being taught’.

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If a piece of reasoning depends upon an illegitimate assumption (or assumptions), then clearly we have solid grounds for rejecting it.

That doesn’t mean that the conclusion drawn will necessarily be false, nor that legitimate reasons might not be given that would provide acceptable grounds for the conclusion, but rather that untested assumptions do not, in their untested state, provide adequate grounds for accepting a conclusion.

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Let's look at another example:

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Original Argument:

[P] Smoking is bad for your health

[C] Therefore you should quit

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The assumption (or ‘suppressed’ middle premise) from this argument is:

If something is bad for your health, you quit it.

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However, other possible assumptions for this argument might be:

• That smokers value their health more than they value the pleasures of smoking.
• That the desire for good health is greater than the addiction to nicotine.
• That smoking is a rational, rather than a compulsive habit (etc.)!

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Our new argument, were we to take into account all these assumptions, would now be:

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[P1] Smoking is bad for your health.

[P2] If you value your health more than you value the pleasures of smoking and

[P3] Your desire for good health is greater than your addiction to nicotine and

[P4] You see your habit as a rational, rather than compulsive one (etc.)

[C] Then you should quit!

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Do you think these new assumptions have strengthened or weakened the original argument...?