Defined:

Modalities are words which indicate the level of certainty with which a claim can be made.

Explained:

Every claim has some probability of being true. Some claims are true beyond any reasonable doubt. For instance, we are quite certain that the earth is roughly a sphere. Other claims are not so certain. For instance, "There is life on other planets." There might be, but no one really knows. If someone says, "There's no doubt about it, there is life on other planets," they used a modality which is too high. If someone says, "There's no doubt about it, there is life on Earth," they've used an appropriate modality. "There's no doubt about it" is the modality in this case.

It is important to use the proper modality. You don't want to overstep your evidentiary limits. In other words, don't say "certainly" if you can't prove the claim with certainty.

High Modalities

When someone uses a high modality, they are saying that the truth of the claim is certain.

Examples of high modality indicators;

• Certainly, definitely, there is no doubt about it, without question, absolutely, for sure, beyond a doubt, positively, necessarily

Examples of sentences with high modalities.

• No question about it, the car needs a valve job.
  
• Absolutely, the defendant was not at the scene of the crime.
  
• All men are mortal (Note that the absence of any qualifying words indicate a high modality.)

Important Note: Claims with high modalities require deductive arguments to prove them.

Low Modalities

When someone uses a low modality, they are saying that the truth of the claim is likely, but not certain.

Examples of low modality indicators;

• Probably, possibly, there's a good chance that, perhaps, maybe, more than likely, might be

Examples of sentences with low modalities.

• I will probably go to Yale when I finish junior college.
  
• There might be life on other planets.
  
• There's a chance of rain by morning.

Important Note: Claims with low modalities require only inductive arguments to support them.

Degrees of probability

• High modalities are limited to certainty. But there is quite a range for low modalities from almost certain to almost impossible. Here's a guideline for the range of low modalities:
  
  
• 99% ± Virtually certain: overwhelming evidence in its favor. Example: The law of gravity
  
• 90% ± Highly probable: very good evidence in its favor.
  
• 70% ± Probable: sufficient evidence in its favor. Example: Most medicines have to pass this test to be approved.
  
• 50% ± Possible: either no evidence or equal evidence for both sides. The Packers will kick off this Sunday. (A coin toss determines which team kicks off just before the game.)
  
• 30% ± Improbable: insufficient evidence in its favor. Example: That numerology helps people rise to fame and fortune.
  
• 10% ± Highly improbable: very little evidence in its favor. Example: The theory that Jesus spent his early years studying with a Hindu guru.
  
• 1% ± Virtually impossible: almost no evidence in its favor. Example: The existence of unicorns.