"Plagiarism" covers very different things, from deliberate copying to a forgotten bracket. Most codes of conduct do not treat them alike either. Here are the types, ordered roughly by how heavily they weigh.
1. Verbatim copying
Text taken straight from a source without quotation marks and without a citation. The classic form and the easiest to prove: searching a single sentence in quotation marks usually finds the source in seconds.
Severity: high. There is rarely doubt about intent when whole paragraphs are identical.
2. Mosaic plagiarism
Sentences and phrases from a source woven into your own text with the odd word swapped. Also called patchwork.
This is the one most people fall into without meaning to — usually because notes were written too close to the original, and later nobody can remember what was quotation and what was their own.
Severity: high. Swapped words are often read as an aggravating factor: it suggests someone tried to disguise it.
3. Paraphrase without citation
The source's idea and structure rendered in your own words, but with no mention of the source. The language is yours; the thought is not.
Many people believe rewording removes the need to cite. It does not — the citation is for the idea, not the phrasing.
Severity: medium to high, depending on extent.
4. Self-plagiarism
Reusing your own previously submitted work without saying so. It sounds harmless, but most institutions treat it as a separate offence — you receive credit twice for the same work.
Severity: varies widely. A formality in some places, equivalent to ordinary plagiarism in others.
5. Wrong or invented sources
A citation that does not support what it is attached to — or a source that does not exist at all. The latter has become far more common since language models arrived, because they invent plausible references.
Severity: high, and rising. A fabricated source is hard to explain away as an oversight.
6. Missing quotation marks
The source is cited, but the verbatim text sits without quotation marks, so it reads as a paraphrase. The reader is led to think the phrasing is yours.
Severity: low to medium. Often genuine sloppiness, and usually handled as such — but it still has to be fixed.
7. Unintentional plagiarism
You remember a phrase without remembering where it came from. It happens to everyone who reads heavily in a narrow field.
Severity: low in intent, but the consequence depends on extent. No code of conduct requires intent to be proven.
What to do about it
Most cases come from one of two working habits, and both can be changed:
- Write notes in your own words from the start. If you paste something verbatim into your notes, add quotation marks and a page number immediately. That is where mosaic plagiarism is born — not at the desk, but in notes taken weeks earlier.
- Add the citation at the same time as the sentence. "I will find the source later" is the habit that produces the most missing references.
A plagiarism check before submission catches the verbatim types — copying, mosaic and missing quotation marks. It does not catch paraphrase without citation, because there is no verbatim text to find. That part you have to watch yourself.