Students often describe forensic science as “the memorization class.” They picture endless lists of words — latent, minutiae, presumptive, individualization — layered on top of procedures, and they brace for a year of flashcards. That picture is wrong, and it is wrong in a way that matters. Forensic Science vocabulary is not a random pile of words. It is a precise system: nearly every term marks a careful boundary between what the evidence shows and what it can actually prove.
Once you know what each term marks, you stop memorizing and start reasoning. A student who knows that a presumptive test can only suggest — never confirm — will never overstate a result. A student who knows that class characteristics narrow a group while individual characteristics point to a source will always say exactly what a comparison has earned. Getting the word right is getting the certainty right, and that is the whole discipline.
Why the exact word matters
Consider the alternative. If you use “match” as a loose, all-purpose word, every result starts to sound like proof — which is exactly how overstated evidence leads to wrong conclusions. But the trained analyst has a graded vocabulary: a result can be consistent with a source, or the source cannot be excluded, or in rare cases a feature is specific enough to support individualization. Each phrase claims a different, carefully bounded amount of certainty. The word is the claim — and the wrong word is a false claim.
This is the difference between sounding certain and being accurate. We ask students in this course to keep a running vocabulary page at the back of the case notebook and to add to it every time a new term of art appears — with a one-line note on exactly what that term does and does not claim. By the second unit, the page does most of the work that flashcards used to do.
Don’t just learn the word. Learn the exact boundary it draws — between what the evidence shows and what it proves.
The core vocabulary
Below is the working set — the terms that appear again and again across crime scenes, fingerprints, trace evidence, blood, and DNA. Learn these first. They earn their keep within the first month.
| Term | Meaning | Where it appears | What it tells you |
|---|---|---|---|
| Locard's exchange principle | every contact leaves a trace | Crime scene & evidence | The founding idea — two objects in contact exchange material, so a scene almost always holds transferable evidence. |
| chain of custody | the documented history of an item | Every unit | The unbroken record of who held the evidence and when — a single gap can make it inadmissible. |
| class characteristics | features shared by a group | Fingerprints, trace | Narrow the field to a category (a shoe size, a fiber type) but cannot point to one source. |
| individual characteristics | features unique to one source | Fingerprints, toolmarks | Fine details that can point to a single source — the basis for individualization. |
| individualization | linking evidence to one source | Fingerprints, DNA | The strong claim that evidence came from one specific source — reserved for the rare cases the features justify. |
| latent print | a print invisible to the eye | Fingerprints | Left by natural skin oils — must be developed with powder, chemicals, or an alternate-light source to be seen. |
| patent print | a visible print | Fingerprints | Left in a substance like ink or dust — visible without any development. |
| plastic print | an impression in a soft surface | Fingerprints | Pressed into a pliable material such as wax or putty, leaving a three-dimensional mark. |
| minutiae | the fine ridge details of a print | Fingerprints | Ridge endings and bifurcations compared point-by-point between a latent print and a known one. |
| presumptive test | a screening test | Blood, chemical analysis | Can only suggest what a substance is — a positive result narrows possibilities but never confirms. |
| confirmatory test | a definitive test | Blood, DNA | Identifies a substance with high specificity — the step that supports a strong claim a presumptive test cannot. |
| trace evidence | tiny transferred material | Trace evidence | Hairs, fibers, glass, soil — small, easily missed, and usually class-level rather than individualizing. |
| chromatography | separating a mixture into parts | Chromatography & analysis | Pulls a mixture (ink, dye) apart into its components so their pattern can be compared. |
| Rf value | a component's travel ratio | Chromatography | The distance a component moves divided by the distance the solvent front moves — a repeatable number for comparing samples. |
| blood typing (ABO) | sorting blood into groups | Blood & bodily fluids | Places a sample in a broad group — a class characteristic that can exclude, but cannot identify one person. |
| spatter / angle of impact | the shape and angle of a drop | Blood & bodily fluids | The geometry of a stain, read carefully, can suggest how and from where a drop traveled. |
| DNA profile / STR | a pattern of repeated DNA markers | DNA & biological | A set of short repeated sequences (STRs) that varies between people — the strongest biological comparison available. |
| match probability | how likely a random match is | DNA | A statistic, never proof — it states how rare a profile is, so a “match” is always a likelihood, not a certainty. |
| exclusion | ruling a source out | DNA, fingerprints | Often the most certain result available — the evidence definitively does not come from a given source. |
| striations / toolmarks | the fine scratch patterns a tool leaves | Ballistics & toolmarks | The marks a barrel or tool cuts into a surface, compared under a microscope to link — or exclude — a source. |
High-value clusters by unit
It helps to learn terms in the company they keep. The same handful of ideas recur within each unit, so a student who masters one cluster has effectively pre-read the vocabulary for the weeks ahead.
Crime scenes & fingerprints. The opening units lean on Locard's exchange principle, chain of custody, class vs. individual characteristics, and the latent / patent / plastic print family. Knowing these turns scene processing and print comparison into a connected web rather than separate facts — and minutiae and individualization decode from there.
Trace evidence & chemical analysis. This unit is built on trace evidence, chromatography, Rf value, and the presumptive vs. confirmatory distinction. A student who internalizes these can say exactly what a separated sample or a screening test does and does not establish.
Blood & bodily fluids. The blood unit turns on presumptive and confirmatory tests, blood typing (ABO), and spatter and angle of impact. Each term marks how strong a claim the evidence supports — and blood typing's class-level limit is the honest boundary the whole unit respects.
DNA, ballistics & the courtroom. The back half of the course returns to DNA profile / STR, match probability, exclusion, and striations and toolmarks. Profile, match probability, and exclusion all tie back to the same idea the whole course turns on — a result is a likelihood the analyst reports, never a verdict the analyst delivers.
How to actually use this
Don’t try to swallow the table in one sitting. Keep this page open during reading and lab, and each time you hit an unfamiliar term, say what it claims out loud before you look it up — and, just as important, what it does not claim. State the boundary, then check. That small act of retrieval is what fixes the term in memory. Within a few weeks the habit becomes automatic, and the “memorization class” quietly turns into a class you can reason your way through — leaving your effort free for the part of forensic science that actually rewards it: judging what the evidence honestly supports.