1. Allusion, Illusion:
An Allusion is an indirect reference. An illusion is a misconception or false impression. Did you catch my allusion to Shakespeare? Mirrors give the room an illusion of depth.
2. Climactic, Climatic:
Climactic is derived from climax, the point of greatest intensity in a series or progression of events. Climatic is derived from climate; it refers to meteorological conditions. The climactic period in the dinosaurs' reign was reached just before severe climatic conditions brought on the ice age.
3. Than, Then:
Than is a conjunction used in comparisons; then is an adverb denoting time. That pizza is more than I can eat. Tom laughed, and then we recognized him.
Than is used to compare; both words have the letter a in them.
Then tells when; both are spelled the same, except for the first letter.
4. There, Their, They're:
There is an adverb specifying place; it is also an expletive. Adverb: Sylvia is lying there unconscious. Expletive: There are two plums left. Their is a possessive pronoun. They're is a contraction of they are. Fred and Jane finally washed their car. They're later than usual today.
If you are using there to tell the reader where, both words have h-e-r-e. Here is also a place.
If you are using their as a possessive pronoun, you are telling the reader what
"they own. Their has h-e-i-r, which also means heir, as in someone who inherits something. Both words have to do with ownership.
They're is a contraction of they are. Sound out they are in the sentence and see if it works. If it does not, it must be one of the previous versions.
5. Lie, Lay:
Lie is an intransitive verb meaning to recline or rest on a surface. Its principal parts are lie, lay, lain. Lay is a transitive verb meaning to put or place. Its principal parts are lay, laid.
Hint: Chickens lay eggs. I lie down when I am tired.