Several words in our language can be spelled as one word or as two, depending on its meaning. Below is a list of a few such words, with sample sentences on how they are used.
Almost - all most
The plane was almost (nearly) three hours late.
We are all most pleased (all very much pleased) with the new schedule.
Already - all ready
The order had already (previously) been shipped.
The order is all ready (all prepared) to be shipped.
Altogether - all together
He is altogether (entirely) too lazy to be a success.
The papers are all together (all in a group) on your desk.
Always - all ways
She has always (at all times) done good work.
We have tried in all ways (by all methods) to keep our employees satisfied.
Anytime - any time
Come see us anytime you are in town, (one word meaning "whenever").
Did you have dealings with him at any time in the past? (Two words after a preposition such as at.)
Anyway - any way
Anyway (in any case), we can't spare him now.
If we can help in any way (by any method), please let us know.
Awhile - a while
One word as an adverb; two words as a noun.
You may have to wait awhile. (Adverb.)
You may have to wait for a while. (Noun; object of for.)
Everyday - every day
You'll soon master the everyday (ordinary or daily) routine of the job.
He has called every day (each day) this week.
Into - in to
He walked into the outer office. (Into implies entry.)
He came in to see me. (In is part of the verb phrase came in; to is part of the infinitive to see.)
Indifferent - in different
She was indifferent (not caring one way or the other) to the offer.
He like our idea, but he wanted it expressed in different (in other) words.
Maybe - may be
Maybe is an adverb; may be is a verb.
If we don't receive a letter from them today, maybe (an adverb meaning perhaps) we should call.
He may be (a verb) out of town next week.
Onto - on to
He lost control of the car and drove onto the sidewalk. (Onto implies movement toward and then over.)
Let's go on to the next problem. (On is an adverb in the verb phrase go on; to is a preposition.)
Someday - some day
Please set up a meeting with them someday next week.
Please set up a meeting with them for some day next week. (Two words when used as the object of a preposition such as for.)
Sometime - some time
The order will be shipped sometime (at some unspecified time) next week.
It took me some time (a period of time) to complete the job.
Whoever - who ever
Whoever (anyone who) is elected secretary should write that letter at once.
Who ever made such a statement? (Ever is an adverb.)
At times you'll find two words spelled as one, and the resulting one word is not a word at all, (a good example is alot). Our language has many such situations, rules, and exceptions to rules. This is why many people feel intimidated and frustrated by grammar.
Source: The Gregg Reference Manual