What makes one consonant different from another?

Consonant parameters

What makes one consonant different from another?

Consonants involve constrictions, or gestures that narrow the vocal tract at a particular point. Most consonants use only one constriction, but some have more than one. In order to fully describe a consonant sound, we need to describe each constriction as well as some other properties of the vocal tract.
Parameters of a constriction gesture

1. active articulator: What articulator moves to make the constriction?
2. passive articulator: What articulator does the active articulator touch or approach?
3. degree of constriction: How close do the active and passive articulators get to each other?
4. (laterality)

These should be specified for every constriction involved in a consonant. The following properties don't apply to any particular constriction, but to the consonant as a whole:
Other parameters

1. state of the glottis: What are the vocal cords doing?
2. nasality: Is air escaping through the nose?
3. airstream mechanism: How is the flow of air being produced?

Answering each of these questions about the state of the vocal tract is enough to uniquely identify any consonant. If two consonants are different, they must differ in their answers for at least one of these questions.

Together, the active and passive articulator are often referred to as the place of articulation (POA). The other parameters are often lumped together and referred to as manner of articulation.