Rule: When the culprit has to serve two or more penalties, he shall serve them simultaneously if the nature of the penalties will so permit; otherwise, in the imposition of the penalties, the order of their respective severity shall be followed so that they may be executed successively. (Material Accumulation System- absolute accumulation of crimes and penalties and establishes no limitation whatsoever and, accordingly, all the penalties for all the violations were imposed even if they reached beyond the natural span of human life. (Guevara))
Threefold Rule- the maximum duration of the convict’s sentence shall not be more than threefold the length of time corresponding to the most severe of the penalties imposed upon him. No other penalty shall be inflicted after the sum of those imposed equals the said maximum period. Such maximum penalty shall in no case exceed forty year. (Juridical Accumulation System- the service of the several penalties imposed on one and the same culprit is limited to not more than three-fold the length of time corresponding to the most severe and in no case to exceed 40 years.)
Duration of the convict’s sentence refers to several penalties for different offenses, not yet served out.
Subsidiary imprisonment forms part of the penalty. (Bagtas vs. Director of Prisons, 84 Phil. 692, 698)
Other system of penalty- Absorption system (the lesser penalties are absorbed by the graver penalties. Observed in the imposition of complex crimes (Art 48), continuing crimes, and specific crimes like robbery with homicide, etc.)
 Par. 1, Art. 70, RPC
 Par 2, Art. 70, RPC.
 Par. 4 and 5, Article 70, RPC