Definition
Intervention logic is the causal chain that explains how and why a programme's activities are expected to lead to desired outcomes. It maps the logical sequence from inputs through activities, outputs, and outcomes to impact, showing the "if-then" reasoning that underpins programme design. At its core, intervention logic answers the question: "If we deliver these activities, then we expect these outputs, which should lead to these outcomes, because [assumptions]."
Intervention logic is the backbone of both theory of change and logframe approaches. While a theory of change is a broader analytical process that includes context analysis and evidence assessment, the intervention logic is the specific causal pathway that emerges from that analysis. It is also the structural foundation of a results chain, providing the logical sequence that indicators must measure.
Why It Matters
A well-articulated intervention logic transforms programme design from a list of activities into a testable hypothesis about how change happens. Without explicit intervention logic, programmes risk implementing activities that are poorly connected to intended outcomes, making it impossible to understand why results are achieved or not. The intervention logic serves three critical functions: it guides indicator selection by identifying what needs to be measured at each level of the chain; it makes assumptions explicit so they can be monitored and tested; and it provides a clear narrative for communicating programme rationale to donors, stakeholders, and communities.
When intervention logic is weak or implicit, monitoring data becomes a collection of disconnected metrics rather than evidence about whether the programme's causal theory is holding. Strong intervention logic turns monitoring into a learning system where data can confirm or challenge the programme's assumptions about how change happens.
In Practice
Intervention logic appears in several forms across different M&E frameworks. In a logframe, it is the vertical logic column showing the hierarchy of objectives. In a theory of change, it is the central causal pathway diagram. In a results framework, it is the structured set of outcome indicators arranged in logical sequence.
A typical intervention logic diagram contains:
- Inputs: Resources required (funding, staff, expertise)
- Activities: What the programme does (training, construction, advocacy)
- Outputs: Direct, tangible products or services delivered
- Outcomes: Short-term and intermediate behaviour or system changes
- Impact: Long-term, broader change the programme contributes to
- Assumptions: Conditions that must hold true at each link
- Risks: External factors that could disrupt the pathway
The intervention logic should be developed early in programme design, before activities are finalized. It is tested through context analysis and evidence review, then operationalized through monitoring frameworks that track progress along each link in the chain. When monitoring reveals that an assumption has failed (e.g., "community leaders will support implementation" when they do not), the intervention logic must be revised, either by addressing the assumption or by redesigning the pathway.
Related Topics
- Theory of Change, The broader analytical process that produces the intervention logic
- Logframe, The operational framework built on intervention logic
- Results Chain, The sequence of results the intervention logic connects
- Programme Logic Model, A visual representation of intervention logic
- Causal Chain, The underlying concept of sequential cause-and-effect
- Assumptions, Conditions that must hold for the logic to work
- Risks, External factors that could disrupt the intervention logic