Raise or rise?

Compare these two sentences:
The prices are rising.
They are raising the prices.
These two verbs are often confused because they look similar but, in fact, they are quite different.
When you raise something, you lift it to a higher position or increase it. When someone or something rises, they move from a lower to a higher position. Rise can also mean to increase in number or quantity.
Raise is a regular, transitive verb, which means that it is always followed by a direct object:
The little girl raised her hand.
In this example, "her hand" is the direct object. If you don't add a direct object, the meaning of the sentence is not complete. If you just say: "The little girl raised", people would expect you to say something else to complete the sentence.

The little girl raised her hand
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On the other hand, rise is an irregular, intransitive verb, so it is never followed by a direct object. Something rises, but you cannot rise something. Examples:
The temperature is rising.
The sun rises in the east.
The past tense of this verb is rose, and the past participle is risen.

The sun rises in the east
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Another verb that can get confused with these two is arise. It is intransitive and irregular too (arise, arose, arisen), but much more formal than rise. It can also mean "get up", but rise is preferred for literal meaning, while arise is mostly used with figurative meaning: They are trying to deal with the problems that arise from immigration. A new crisis has arisen.

Let's have a look at a few collocations and idioms:

RAISE

• Raise your voice: shout. Don't raise your voice like that, please. I'm not deaf!
• Raise money / funds / a loan means to collect money. They are raising money for charity.
• Raise a child means to bring up a child. They raised her daughter as a Catholic.
• Raise animals: take care of or breed animals They raise chickens on their farm.
• Raise your glass to somebody means to hold up your glass and wish them happiness or good luck before you drink. 
• Raise hell is to protest angrily or cause a considerable disturbance.
• Raise the roof is to produce a lot of noise in a building.
• Raise the salary.
• Raise the flag.

Raise your glass
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RISE

• Rise early: He rises early every day.
• Rise to one's feet is to stand up.
• Rise to the occasion / challenge: to show that you are able to deal with an unexpected situation.
• A river rises where it begins to flow. The Thames rises in the Cotswolds.
• If mountains rise in the distance, they become visible.
• Rise from the ashes is to come to life again.
• Rise to power. Adolf Hitler's rise to power began in 1919.
• Rise and fall. Today we've studied the rise and fall of the British Empire in our History class.
• Rise through / from the ranks is to work one's way to the top. She rose through the ranks to become managing director.
• Your hair rises when you feel cold or frightened.
• If your spirits rise you get happier.

Check what you have learnt by doing this exercise:

Note: if you cannot see the exercise above, try this link.

Finally, let's relax with this beautiful song by Craig David, featuring Sting, called "Rise and fall"