This paper develops a theoretical model for the semantics of connectives, following central ideas of Reichenbachian tense semantics. In a first step, the terminological and conceptual framework is presented and illustrated with German 'da'. The meaning of a connective is modeled as a four-place-relation between the situated object E, a reference object R, a discourse anchor S and the speaker O. The relata can belong to one of four different classes of entities: physical object, event, proposition or act. Correspondingly, the relations are divided into four cognitive domains: space, time, alethics/epistemics, and deontics. In each domain, relations can be treated under three different perspectives: situation, condition or causation. A cross-classification of relational domains and perspectives provides a typology of connectives which is more consistent than the ones available in traditional grammar. In the second part of the article, the analytic apparatus is refined, using German 'so' as the main example. Following Roman Jakobson, a distinction is made between contiguity and similarity relations. Contiguity relations are typically encoded by functional categories, whereas similarity relations are encoded by lexical categories. However, there are a few connectives like so which encode similarity relations. A structural isomorphism between similarity and contiguity relations makes it possible to reinterpret so in certain contexts as an indicator of contiguity. In these cases, so is semantically weakened, particularly in relation to its definiteness. The model is extended to 'also', from which 'als' descends etymologically. The third part of the article contains the semantic characterization of 'als' in its variants as an intransitive and transitive connective. 'Als' is described paradigmatically, in terms of the semantic oppositions that distinguish it from 'da', 'so', 'wie' and 'wenn'. Like 'so', it originally encodes similarity relations, but in present day German its use has been extended, so that it may indicate contiguity relations as well. With 'da' and 'so' it shares the abstract relational meaning O-S,R,E. The main difference from 'da' is its lesser degree of definiteness; in contrast to 'so', its use is almost exclusively temporal. 'Wie' and 'wenn' are indefinites, i.e. they do not establish a deictic backlink to the speaker and discourse context. Als indicates that the situated event temporally overlaps with a specific event of reference, whose factivity is presupposed. The reference event must be categorically predictable in the context of utterance. 'Als' does not indicate temporal antecedence of the reference event in relation to the speech event; it only requires the identifiability of the reference event and its non-coincidence with the speech event. In the last section, so-called "peripheral temporal clauses" are examined with respect to the syntagmatic interaction between aspectuality, intonational focus, serialization of clauses and the abstract relational meaning of 'als'. The proposed semantic formula is shown to be capable not only of clarifying the paradigmatic structure of a subset of German connectives but also of explaining the semantic and stylistic properties of complex sentences.