Chapter XXVIII: Part I: (pp. 1-22), which is sometimes designated De Utililate

Scientiarum_, treats of the four _offendicula_, or causes of error. These are, authority, custom, the opinion of the unskilled many, and the concealment of real ignorance with pretence of knowledge. The last error is the most dangerous, and is, in a sense, the cause of all the others. The _offendicula_ have sometimes been looked upon as an anticipation of Francis Bacon's _Idola_, but the two classifications have little in common. In the summary of this part, contained in the _Opus Tertium_, Bacon shows very clearly his perception of the unity of science and the necessity of encyclopaedic treatment.