Do you mean "Can you add 'less' or 'ful' to a word to turn it into an adverb?' If that's what you mean, the answer is no. You form adverbs by adding 'ly'. for example 'slow' becomes 'slowly' If you are talking about adjectives, rather than adverbs, then yes, you can add 'less' to make an adjective meaning 'without this.' Somebody without a voice is voiceless, somebody without teeth is toothless, somebody without legs is legless. (NB note that the first part of the word - the noun - is in the singular. We say 'toothless' (not teethless) and 'legless' (not legsless). And yes, the adjective which is the opposite of '-less' is sometimes formed with '-ful. This is the case with abstract nouns, such as 'hope' and 'care' ie hopeless/hopeful and careless/ careful. But this doesn't work with all adjectives - there are many ways of forming adjectives, and you do have to learn each word individually. I hope is the right answer to the question you wanted to ask.