Indicatives are typically defined in opposition to counterfactual conditionals, which have extra grammatical marking which allows them to discuss eventualities which are no longer possible.
Although this analysis covers many observed cases, it misses some crucial properties of actual conditional speech and reasoning.
Grice, Frank Cameron Jackson, and others attempted to maintain the material conditional as an analysis of indicatives' literal semantic denotation, while appealing to pragmatics in order to explain the apparent discrepancies.
[1] Contemporary work in philosophical logic and formal semantics generally proposes alternative denotations for indicative conditionals.
People readily make the modus ponens inference, that is, given if A then B, and given A, they conclude B, but only about half of participants in experiments make the modus tollens inference, that is, given if A then B, and given not-B, only about half of participants conclude not-A, the remainder say that nothing follows (Evans et al., 1993).