A sentence is a unit of words, put together for a single purpose; just as a group of related people is called a family unit.
You may find it easier to think of what belongs in a sentence as being similar to a family unit.
Siblings are closest, so they can be joined by the comma and/or a joining word (a conjunction, such as 'and').
First cousins are not quite so close, but still related well enough to put them into the same sentence; they can be joined with a semicolon.
Second cousins are still related, but further away.
They could fit into the same paragraph, but not the same sentence.
Past that, however, and you need not just a new sentence, but a new paragraph, or perhaps a whole different article.
Re-read the above two paragraphs and you will see I have demonstrated what I was explaining.
While most people can recognise a sentence when they see one, not so many writers know when to stop one sentence and move on to another.
There is no need to be economical with that little dot - known as the full stop or period - and try to fit far more into a sentence than belongs there.
There are two major faults I've noticed in sentences.
One involves the over-use of the comma in which one thought follows another, within the same sentence, like a list of unrelated thoughts joined only by the comma.
(The correct name for what I have simply termed 'thoughts' is the 'independent clause'.
It means a clause - a group of words including subject, verb and supporting words - that makes sense on its own.
) This is an admittedly extreme example of such a sentence: 'My cat brought a frog into the house last night, there's a worm-hole in my apple, and my jacket is too long.
' They are simply a list of obviously unrelated thoughts put together with commas between them and a full stop at the end.
The second fault is also a list of thoughts, but incorrectly joined, and usually caused by an attempt to blend unrelated or semi-related thoughts together, using incorrect or absent punctuation.
• There may be a comma where a semi-colon or a full stop would be better.
• There may be no commas or other punctuation at all.
• There may be a comma, but no joining words (conjunctions), such as 'and',' so', 'but', or 'because'.
• Parts of one sentence may be missing, and the missing part blended into another sentence so that neither makes sense.
When you are writing sentences, and you are not sure how much to fit in there; think about the relationships between the separate thoughts you are trying to include, just as in the family analogy I used.
How close are they? Would they make more sense if they were separated? These incorrect sentences are mostly due to the way we speak.
We don't speak in sentences and paragraphs; we link our thoughts together with pauses until we finish what we are saying.
We speak in fragmented and run-on sentences quite commonly.
If we try to write like this, however, we will construct sentences that don't make much sense.
Verbal communication must be translated into the written form, and thus we have punctuation marks.
Make good use of them so that your readers understand you clearly.
Whether or not you write a long sentence or a short one, it should all fit together as a cohesive whole.
The sentence is your writing unit.
Keep it simple.