The paper defends a naturalistic version of modal actualism according to which what is metaphysically possible is determined by dispositions found in the actual world. We argue that there is just one world – this one – and that all genuine possibilities are grounded in the dispositions exemplified in it. This is the case whether or not those dispositions are manifested. As long as the possibility is one that would obtain were the relevant disposition manifested, it is a genuine possibility. Furthermore, by starting from actual dispositional properties and branching out, we are able to countenance possibilities quite far removed from any state of affairs that happens to obtain, while still providing a natural and actual grounding of possibility. Stressing the importance of ontological considerations in any theory of possibility, it is argued that the account of possibility in terms of dispositional properties provides a more palatable ontology than those of its competitors. Coming at it from the other direction, the dispositional account of possibility also provides motivation for taking an ontology of dispositions more seriously.

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In order to evaluate seismic vulnerability of existing reinforced concrete buildings, a simplified approach is proposed to take into account the beam-column joints shear collapse. This collapse is described by a link element which is introduced between column and beam. To develop and verify this element, several comparisons have been performed with experimental results of laboratory test and numerical results obtained by a two-dimensional finite element model specifically carried out for this check. The link element uses a tri-linear moment-rotation law, compatible with standard Italian and European codes, whose features can be estimated by limited structural and geometrical information, which is a typical situation on older existing structures, and by standard code recommendations. In order to give a preliminary evaluation of the seismic capacity for existing R.C. frames, taking into account the beam-column joints behaviour, this link element has been introduced in a one-dimensional model of bearing structure of the Unit N.1 of the Santa Maria Annunziata Hospital in Florence (Italy) and pushover analyses have been carried out.