It is argued in this brief paper that the so-called Indo-European 'contrastive' suffix *-(t)er(o)- of adjectives and adverbs derives ultimately from the contamination and subsequent grammaticalization of deictic particles in *(e/o)t and *(e/o)r. The original function of this suffix was, therefore, not contrastive, but rather locational, in nature. It is also proposed here that although the comparative suffix *-tero- of Greek and Sanskrit can be traced etymologically to the contamination of the same deictics, it is the result of a very different evolutionary process.