Nonideal

Nonideal is an adjective used in many disciplines to describe systems, models, or objects that deviate from a commonly assumed ideal or simplified form.

In thermodynamics and physical chemistry, a nonideal or real gas deviates from the ideal gas law. Deviations grow with pressure and with intermolecular forces; models such as the van der Waals equation and virial equations introduce corrections. The compressibility factor Z = PV/(nRT) quantifies departures from ideal behavior.

In electronics, nonideal components exhibit parasitic elements and non-linear behavior. Resistors have tolerance and noise; capacitors and inductors possess parasitic capacitance and inductance and frequency dependence; active devices have finite gain, offset voltages, leakage currents, and temperature effects.

In philosophy and political theory, nonideal theory concerns principles of justice and ethics under real-world conditions, such as persistent injustice, imperfect compliance, and institutional constraints, rather than under idealized assumptions. In economics and engineering, analyses often address nonideal frictions, information gaps, and resource constraints.

The term is context-dependent and is used to emphasize departures from idealizations in theory or practice. Where ideal models provide clarity and tractability, nonideal considerations aim to improve realism, prediction, and applicability across disciplines.