Learn English – “Shepherding” vs. “sheepherding”

@RegDwight is correct in every particular. Till is indeed older and the two can be used pretty much interchangeably.

There is really only one usage I can think of where you would not use till: in setting up a negative conditional.

Until my landlord fixes the plumbing, I am not going to pay the rent.

I am not going to pay the rent until my landlord fixes the plumbing.

Here it would sound strange to use till, and I'm not really sure why. Perhaps it is the negative.

One more thing. Sometimes you will see people spell till as a contraction of until: that is, as 'til. This is simply wrong, and not seen outside of old poetry and modern greeting cards aiming for a "poetic" tone. Anywhere you see 'til being used, till would be the correct word.

Illusion

1. Illusion is a kind of wrong perception.

2. In illusion, an external stimulus is always present. In other words, illusions are caused by external stimulations.

3. Illusion is almost universal.

4. Normal persons suffer from illusions.

5. The same situation arouses the same type of illusion in most people.

Hallucination

1. Hallucination is a false perception.

2. In hallucination, no external stimulus is present. Hallucinations are caused by internal stimulations.

3. Hallucination is a personal experience.

4. Hallucinations are mostly confined to mentally ill persons and to those people under the influence of drugs. The character of hallucination is determined by the individual's present and previous experiences.

5. The same situation may not arouse hallucination in all. There are individual differences with regard to hallucination. The same individual may experience different hallucinations are different occasions also.

Source.