Plenary vs. Partial Indulgence

The comparison

	Plenary	Partial
Effect	Remits all temporal punishment due to sin (when fully gained)	Remits part of that temporal punishment
Difficulty	Demanding: usual conditions plus detachment from all sin	More readily gained through many approved works
Typical conditions	SacramentalGlossaryA sacred sign instituted by the Church—holy water, medals, scapulars, blessings—that disposes the soul for grace; not one of the seven Sacraments. Confession, Holy Communion, prayer for the Pope's intentions, and full detachment from sin (even venial), plus the prescribed work	The prescribed work performed in the state of grace, with at least a general intention to gain the indulgenceGlossaryA remission before God of temporal punishment due to sins already forgiven, granted by the Church from the treasury of merits.
Frequency	Generally one plenary indulgence per day (with noted exceptions, e.g. at the point of death)	Multiple partial indulgences may be gained

What Catholics confuse

"Plenary" does not mean the sin was worse or the prayer was longer. It names the scope of the remission. Many men assume they gain a plenary indulgence because they completed the external work—while remaining attached to a pet sin. Without detachment, the indulgence may be partial only. Conversely, partial is not "weak Catholicism"; it is the ordinary generosity of the Church for daily fidelity.

How to pursue them

Know the work. Know the conditions. Go to Confession. Receive the Eucharist. Pray for the Holy Father. Root out the sin you keep negotiating with. Apply indulgences to the souls in Purgatory—an act of mercy worthy of a Christian man. The Church publishes the norms; follow them rather than internet summaries.