Study materials
In these three sentences the structure is broken, although every word is in place.
The bus was late, we missed the film.
Two full sentences joined by a comma alone.
Because the shop was closed.
Half a sentence with no main clause.
The results, which were obtained under unusual conditions and which the committee had not approved, appear consistent.
Correct, but the subject and verb are too far apart.
This article explains how to join two full sentences, why a part with although or because cannot stand alone, and what to do with an overlong insertion.
How to split a sentence correctly
Two full sentences cannot be joined by a comma alone. A full stop, a semicolon or a conjunction goes between them.
The results appear consistent, further verification is required.
Two sentences joined by a comma.
The results appear consistent. However, further verification is required.
A full stop and a linking word.
The results appear consistent, but further verification is required.
A comma and a conjunction.
When splitting a sentence, keep the link between the parts. If the original had although, the new sentence needs however or but, or the contrast disappears.
A part with although, because or when cannot stand alone as a sentence. Although the sample was small is only half a sentence, and it needs a main clause.
Long sentences
A complex sentence is not a flaw in itself. It gets hard when several embedded parts stand between subject and verb.
The results, which were obtained under unusual conditions and which the committee had not approved, appear consistent.
Subject and verb far apart.
The results appear consistent. They were obtained under unusual conditions, which the committee had not approved.
The long part moved to the end or to its own sentence.
English copes with a long ending far better than with a long insertion in the middle.
Common mistakes
The first mistake is two sentences joined by a comma alone.
The results appear consistent, further verification is required. → The results appear consistent. However, further verification is required.
Two sentences need a full stop or a conjunction between them.
The second mistake is however after a comma between two sentences.
It was raining, however we went out. → It was raining. However, we went out.
However opens a new sentence.
The third mistake is an although clause standing alone.
Although the sample was small. The results held. → Although the sample was small, the results held.
An although clause needs a main clause.
The first and second mistakes show in the comma between two full sentences. If each side of the comma has its own subject and verb and there is no conjunction such as but or so, a full stop or semicolon is needed. However is not a conjunction. The third shows at the full stop after a part with although, because or when. The sentence has not ended there.