There are areas where conditional clauses overlap other adverbial clauses, for instance temporal clauses (already discussed in section 9.1.) or causal clauses, as below:

which conveys a similar meaning to:

The difference lies in the degree of probability: in sentence [1] the speaker is sure that the hearer will attend the party, whereas in [1a] there is only an assumption that the speaker may go. For both sentences attending the party is a necessary condition for “meeting him”. Since can introduce factual/contextual conditional clauses only (cf. sections 5.3. and 8.1).

Yet, the overlap between conditional clauses and clauses of concession is far more considerable. In general, the former reflect the dependence of one circumstance or set of circumstances on another, as in [2]:

whereas the latter imply a contrast between circumstances, meaning that in the light of the circumstance described in the subordinate clause the content of the main clause is surprising (cf. Quirk et al. 1972:745), as below:

The overlap between conditional and concessive clauses occurs when subordinators such as even if are used, expressing both the dependence itself and the surprising character of this dependence: