' - 'similia similibus curentur'.
For example, if you chop up onions your eyes might sting, water and your nose run. In Homeopathy, we have a remedy called Allium Cepa - it is made from a micro dose of onion in a diluted amount to treat people suffering from the well-known symptoms that onions can cause: stinging, watering eyes and sneezing.
Put another way, the 'like cures like' principle states that any substance that causes symptoms to appear in a healthy person (the person chopping the onion), is able to deal with the same symptoms in a sick person (the person suffering with well known symptoms of stinging, watering eyes and sneezing).
