Weak form of the EMH states that all information contained in past prices is partly reflected in prices.

In the weak form of Efficient Markets, chartists and other technical analysts are exploit the weaknesses. 

If weak-form efficiency holds, it is possible for investors using information from past price changes to obtain consistent excess profits.

If semistrong form efficiency holds, it should not be possible for investors using publicly available information to obtain consistent excess profits.

If semistrong form efficiency holds, security analysts and others involved in conducting fundamental analyses with financial statements and other publicly available information are engaging useful activities