EVIL EFFECTS OF FALSE STATEMENTS. 87 



the chemist who supplied us with chemicals, we must test 

 the substances. So-called facts cannot be relied on as facts, 

 unless they have been at one time or another carefully 

 verified. 



In logical phraseology, an assertion in science would 

 be called a ' proposition.' A scientific term standing alone 

 does not express either a truth or untruth, but merely 

 excites in the mind the conscious impression of an object 

 or class of objects. In order, therefore, to express a truth 

 or untruth, we must employ an * indicative sentence ' or 

 proposition. 



Propositions in science, like ideas and terms, often go 

 together in pairs. They may be classed into axiomatic, 

 true and false, uncertain, conditional and unconditional, 

 affirmative and negative, universal and particular, in- 

 definite or ambiguous, universal-affirmative, particular- 

 affirmative, universal-negative, particular-negative, ex- 

 clusive, exceptive, inconsistent, contradictory, contrary, 

 sub-contrary, equivalent, &c. Propositions have also been 

 classed into : 



1. Subjective, or those based upon internal evidence. 



2. Objective, or those based upon external evidence. 



And, 



3. Those based upon both. 



A true scientific statement is one which does not con- 

 tradict' any of the facts or laws of nature, but agrees with 

 and is supported by all of them. Many statements, how- 

 ever, which appear to be true in one state of knowledge 

 are ultimately found to be false, and some which appear to 

 be false are found to be true. A false proposition is one 

 which contradicts those facts or laws. An uncertain 

 statement is one which either has equal or no manifest 

 evidence for or against it. But whilst no scientific idea or 



