TLDR:
The article suggests approaching the field of speculative senior securities through common-stock approach to understand the risk involved. While low-priced bonds and preferred stocks are associated with corporate weakness, they offer contractual obligations that could provide advantages. Working capital and sinking-fund provisions contribute to safety of senior securities. The "rule of maximum valuation for senior issues" states that a senior issue cannot be worth more than a common stock without junior securities outstanding, which helps detect overpriced senior issues.