Alles innerhalb des a-tags bei .hover eine opacity: .6; bekommen ABER...

<section>
                                    <a class="a-modul" href="arbeit01.html">
                                        <h4 class="header-tabelle">
                                            <span class="table-row">
                                                <span class="table-cell">
                                                    Arbeit, 2012
                                                </span>
                                            </span>
                                        </h4>
                                       <figure>
                                          <img src="http://misanthrop.bplaced.net/foo/foo/foo.jpg" alt="Arbeit, 2012">
                                       </figure>
                                    </a>
                                    <p>
                                        Performance
                                        <span>Kunsthalle Münster,</span>
                                        <span>Speicher II, Münster</span>
                                    </p>
</section>

nav a,
      nav a:link,
      nav a:visited {
         background-color: #384d86;
      }
      nav a:hover,
      nav a:focus,
      nav a:active {
         background-color: whitesmoke;
         color: black;
      }
      nav a,
      nav a:link,
      nav a:visited,
      nav p {
         padding: 0.8rem 0;
      }

.a-modul {
         display: block;
         padding: 0.3rem 0;
      }
      .header-tabelle {
         display: table;
         width: 100%;
         height: 2.7rem;
         margin: 0 0 0.8rem 0;
         padding: 0 0.3rem 0 0.3rem;
         text-align: center;
      }
      .table-row {
         display: table-row;
      }
      .table-cell {
         display: table-cell;
         vertical-align: bottom;
         line-height: 1.2rem;
      }
      .arbeiten-galerie div {
         display: flex;
         flex-wrap: wrap;
         justify-content: space-around;
      }

      .arbeiten-galerie>h4 {
         display:none;
         text-align: center;
         margin: 0.3rem 0 0.2rem 0;
      }
      .arbeiten-galerie div>* {
         margin: 0.3rem auto 0.8rem auto;
         flex-grow: 0;
         flex-shrink: 0;
         flex-basis: 400px;
      }
      .arbeiten-galerie div section img:hover {
         opacity: .6;
         -webkit-transition: opacity 0.2s ease-in-out;
         -moz-transition: opacity 0.2s ease-in-out;
         -o-transition: opacity 0.2s ease-in-out;
         -ms-transition: opacity 0.2s ease-in-out;
         transition: opacity 0.2s ease-in-out;
      }