  There is nothing wrong with this view, but it is emphatically not that of Leśniewski. According to him, a definition introduces a new expression into the object language. Again, the proprieties have to be respected, and getting these right turns out to be a tricky matter. Also, it is up to the author of a logical system as to which definitions he or she chooses to introduce. But there is an important difference. Since definitions add new expressions to the object language, they add expressions in places where they can be quantified, and so can enhance the system’s expressive power. Leśniewski admits this option: according to him it is the logician’s job to keep adding to the system. If in the process, new things are provable that were not provable before, so much the better, provided the proprieties are respected. If we can prove a theorem not containing a defined expression after a definition has been introduced that could not be proved before, the definition is said to be creative. Most logicians decry creative definitions: Leśniewski embraced them. Leśniewski contended that the symbol ‘=Def.’ used by most logicians actually sneaks an unrecognized primitive into their work. He thought this of Whitehead and Russell, and it is why he wanted to formulate Protothetic based on equivalence alone, since then the same connective is primitive that is used for definitions. In his view, definitions are object-language equivalences and should be recognized as such. In retrospect we can see that this view was too extreme. There is room for abbreviatory definitions, and indeed Leśniewski “unofficially” used one himself, that of the particular quantifier. What Leśniewski calls ‘definitions’ might better be called ‘definitional axioms’. That these can be added as we go along rather than collected together at the beginning of a logic is simply a feature of his way of doing logic.