Cladistics is a method of phylogenetic analysis that focuses on shared derived characters, also known as synapomorphies, to infer evolutionary relationships. It relies on the principle of parsimony, which states that the simplest explanation is usually the best. In cladistics, the simplest explanation for the distribution of characters is the one that requires the fewest evolutionary changes.

Here's how it works:

1. Character identification: Identify characters (morphological, genetic, etc.) that vary among the taxa being studied.

2. Character state polarization: Determine which character states are ancestral (plesiomorphic) and which are derived (apomorphic).

3. Cladistic analysis: Group taxa based on the shared derived characters they possess, assuming that taxa sharing more derived characters are more closely related.

4. Tree construction: Construct a phylogenetic tree (cladogram) that reflects the relationships inferred from the cladistic analysis.

Cladistics does not consider the strength of the characters, meaning it doesn't account for how much a character varies within a group or how reliable it is as an indicator of evolutionary relationships. This is one of the limitations of cladistics.

Other methods like phenetics consider the overall similarity between taxa, regardless of whether the similarities are due to shared ancestry or convergent evolution.

Let me know if you would like to delve deeper into cladistics or other phylogenetic methods!