In relation to article and content writing, I've ...

Copyscape is a free plagiarism checker. The software lets you detect duplicate content and check if your articles are original. Given the URL or text of the original content, Copyscape returns a list of web pages that contain similar text to all or parts of this content. Learn more about Copyscape.

Copyscape detects similarities in words, order of words, order of sentences and order of paragraphs.

This means that copyscape can be fooled. Some people have tested it and found that indeed it can be fooled. I've read somewhere that if you change every third word of a sentence (change the word into its synonym), the article will have no Copyscape hits whatsoever.

There are software available out there that do this kind of job. They are called article spinners. They spin the article to create a new version of it. Many article marketers use a spinner. It helps them produce hundreds of articles based on a single 'seed' article. Mind you, these 'spun' articles won't have the quality that you are looking for. It doesn't think which is the best synonym to use.

Ex:

Original: I am glad you are fine.
Spun 1: I am jovial you are threadlike.
Spun 2: I am happy you are elegant.

So, the question now is, "Is Copyscape useful?" Yes. "Can it test originality?" Yes. "Can it test if the article makes sense?" No. This is the job for humans, not a computer program.

After running your page URL in copyscape, it automatically produces a result whether you have duplicate contents or not. If you're still unconvinced, you can directly copy and paste each of the sentence in google search. There, you will know and avoid plagiarism.